9 th Grade Young Geoscientists
John A. and Katherine G. Jackson
School of Geosciences
The University of Texas at Austin
Southwest Texas Junior College
9 th Grade Young Geoscientists
Guidebook for Geoscience Field Trip
to Uvalde, Texas Area
Sigrid Clift*
and contributions by
Jay Raney*
June 2006
2007 Guidebook revised by Sigrid Clift
*Sigrid Clift and Jay Raney are scientists at the
Bureau of Economic Geology, Scott W. Tinker, Director.
The Bureau of Economic Geology is a research unit
of the Jackson School of Geosciences.
John A. and Katherine G. Jackson
School of Geosciences
The University of Texas at Austin
Southwest Texas Junior College
9th Grade Young Geoscientists
INTRODUCTION
Welcome to the Young Geoscientists field trip
hosted by Southwest Texas Junior College and
The University of Texas at Austin, John A. and
Katherine G. Jackson School of Geosciences
(fig. 1).
For most of you, this will be your first
geological field trip. Consider it a guided tour
of the geology—a learning experience that’s
both fun and informative. The Uvalde area has
an interesting and diverse geological history.
You will learn about the processes that form the
rocks and the landscapes. You will see evidence
of an ancient ocean and ancient volcanoes. The
Uvalde area is rich in natural resources that
include water and economic mineral deposits
such as basalt and asphalt (fig. 2). We depend
on water in our daily lives, and basalt and
asphalt quarried near Uvalde are used all over
the state as construction materials. During
heavy rainfall, the abundant water resources can
create dangerous flooding and result in damage
to property and the local environment.
Geoscientists play a crucial role in finding
and managing our natural resources and study-
Figure 2. Students from 2006 Young Geoscientists
field trip examine basalt at the Vulcan Knippa Quarry.
ing how to predict and lessen the effects of
geologic hazards that can cause great destruction to life and property. As the world’s population increases, we need more resources from
the Earth and more geoscientists to find them.
We need to protect our environment. We must
choose places to live and work where geologic
hazards—such as floods, earthquakes, volcanic
eruptions, and landslides—do not destroy lives
or buildings.
Each of you will learn to think like a geoscientist, which includes important concepts
such as geologic time and the power of water
to erode rock and deposit sediment. You will
see how detailed observations and ideas can be
used to build a theory of how the Earth developed over millions of years. What we learn at
one place can be used to interpret the observations we make at a new place. The geologic
features similar to those you see in Uvalde can
be observed at many other places in the world.
There will be seven stops at areas of geologic
Figure 1. Students from 2006 Young Geoscientists fieldtrip swim in the Nueces River at Big Oak River Camp.
interest on our field trip. You may have visited
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some of them before, but this time you’ll look
at them as a geoscientist.
• The first stop will be Black Waterhole,
an exposure of one of the many
ancient volcanoes found in this area.
• We will then visit the Knippa Traprock
owned and operated by Vulcan
Materials, where an igneous rock called
basalt is produced for construction
materials. This quarry is located in an
ancient volcano similar to the one we
will visit at Black Waterhole.
• At stop 3, we will visit the Del Rio rock
formation that was formed in a shallow
ocean environment. We will look at the
evidence that leads geologists to this
conclusion.
• Mount Inge and the Leona River will
be our next stop. We will discuss the
volcanic features of Mount Inge and
learn about aquifers.
• We will make a detour to Southwest
Texas Junior College, where you will
experience exciting 3-D animated
models of aquifers and other geologic
features. You will also participate in a
review for a quiz that everyone will
take at the conclusion of the field trip.
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Figure 4. You can do it!
• The evening will be filled with bats
flying out of Bat Cave at the Annandale
Ranch (fig. 3). You will also learn about
how caves are formed at this stop.
On the second day of the field trip, we will
visit two sites:
• Stop number 6 will be a visit to the
Asphalt Quarry owned and operated by
Vulcan Materials. This is an important
natural resource found in the asphalt
belt in Uvalde County.
• Our last stop will be Big Oak River
Camp located on the Nueces River,
where we will have a review and go
for a swim.
We hope that your field-trip experience
is a memorable one and that you will come
away understanding the geology in your
backyard (Uvalde) and the important role that
geoscientists play in our society.
This is a great opportunity to learn how to
think like a scientist. You can do it! (fig. 4)
Figure 3. Students from 2006 Young Geoscientists
field trip enjoyed the visit to Annandale Bat Cave.
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HOW TO USE
THE GUIDEBOOK
UVALDE
GEOLOGIC STORY
Each day we will have an orientation to
talk about where we are going and what we’ll
do and see. We’ll tell you about the important
ideas to be discussed and the words you’ll learn.
The guidebook is your notebook. You can use
it to take notes and draw pictures.
At the back of the guidebook is a chart of
the geologic time scale, a more detailed geologic
time scale for the Uvalde area, a watershed
diagram, a map of the field trip, and a glossary
that defines geologic terms (those in italics
throughout the text). The geologic time scale
has a column for notes, and you are encouraged
to use this space to record the timing of geologic
events or features that we see or discuss. The
map shows the stops we will be visiting. It
helps us see the regional relationship in space of
the many geologic features we’ll visit.
The things that are underlined, set off by
bullets, or otherwise emphasized in the text of
the guidebook are a good place to start when
you’re reviewing for the quiz. There is also a
document at the back of the guidebook that
will provide you with geologic terms you
should know for the quiz.
By Jay Raney
U.T. Bureau of Economic Geology
Geologists study the history of the Earth,
processes that modify the Earth, and Earth
resources. To figure out the history of the Earth
we use many different sources of information.
We study rocks we can see at the surface and
rocks that we know only from deep holes that
we’ve drilled into the Earth, or from images we
take of the subsurface using geophysics.
Deep beneath us, thousands of feet below
the surface, are very old sandstones and shales
and limestones. These are as old as 400 to
500 million years (Geologic Time Scale).
Geologic time is so great that it’s difficult to
appreciate. These very old rocks are related to
the Appalachian Mountains (fig. 5). In Texas
we call these buried mountains the “Ouachitas.”
This part of Texas had a range of mountains
that were formed about 300 million years
ago. The mountains, the Ouachitas, were then
slowly eroded and covered by layers of younger
rocks. You can’t see these very old rocks in the
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Figure 5.
Uvalde through
geologic time.
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Uvalde area, but we know they are there from
deep boreholes.
About 150 million years ago, the Gulf of
Mexico began to form. This part of Texas, at
the margin of the early Gulf, was later flooded
by a warm tropical sea. Sand, shale, and limestone were deposited. This period of geologic
time is called the Cretaceous, and most of the
rocks we see at the surface today are of Cretaceous age (135 to 65 million years ago).
Dinosaurs and other creatures lived along the
edge of the Cretaceous ocean, and other nowextinct plants and animals lived in the ocean.
These animals form interesting fossils, and
they are also part of the source of hydrocarbons. Hydrocarbon is a fancy word for
“fossil fuels.” You might know hydrocarbons
by their other names: oil, natural gas, coal,
lignite, and asphalt. These are the remains of
the countless billions of organisms that lived
and died in the Cretaceous—plants, dinosaurs, clams, starfish, oysters, and tiny microorganisms that floated in the sea.
These Cretaceous rocks are very important.
Have you heard of the Edwards aquifer? The
main water supply for San Antonio and many
other towns in this part of Texas comes from
wells in the Edwards limestone, which is one
of the Cretaceous-age rock formations. The
water is not Cretaceous age. It’s mostly young
water that falls as rain and then seeps deep
underground into the Edwards limestone.
Toward the end of Cretaceous time, about
80 million years ago, there was a new and exciting element added to the environment in
this area—volcanoes! Masses of magma, hot
molten rock, moved from deep in the Earth
(50 or 60 miles below the surface) into the
shallow crust of the Earth in this area near
Uvalde (fig. 5). Some magma broke through
the surface and erupted as volcanoes. The
eruptions included both flows of lava on
the surface, even “lakes” of lava, and violent
explosive eruptions where the hot magma
interacted with water and created shallow craters and eruptions of volcanic ash and rocks.
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Figure 6. Balcones Fault Zone from Uvalde to Dallas.
There were two major areas of volcanoes at this
time, one near Uvalde and a second field of
volcanoes near Austin. During the time of the
eruptions marine sediments (limestone, shale,
and sandstone) continued to be deposited in
and around the volcanoes.
After the Cretaceous the area was uplifted.
This part of Texas that had been at sea level is
now several hundred feet above sea level. After
the Cretaceous and continuing until about
15 million years ago (Miocene), there were a
series of earth-shaking events—earthquakes
(fig. 5). The earthquakes were caused by
breaks in the Earth where the rocks to the
south and east (toward the Gulf Coast) moved
down relative to those to the north and west
(Texas Hill Country). Movement along
these breaks, which geologists call “faults,”
was probably just a few feet or less for each
earthquake. Many earthquakes over millions
of years add up to hundreds of feet of movement (“displacement”) on the larger faults.
The faults form a system of faults that extends all the way to Dallas (fig. 6). These
faults are called the Balcones Fault Zone.
The Balcones Fault Zone separates the Gulf
Coastal Plain from the Texas Hill Country.
The faults and related fractures are important
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because they are areas where surface water can
flow deep into the subsurface to recharge the
Edwards aquifer.
A result of the Balcones faulting was that
the uplifted interior of Texas became an area of
erosion. Creeks and rivers eroded valleys in the
Texas Hill Country. The sediments carried by
these streams crossed the Balcones Fault Zone
and ran onto the coastal plain and eventually
to the Gulf of Mexico. On the coastal plain,
the streams flowed on a lower slope; they
flowed more slowly and could not carry all the
sediment. As a result thousands of feet of clay,
sand, and gravel were deposited on the coastal
plain or in the Gulf of Mexico.
And now? Now we take advantage of all this
geologic history. Texans farm the rich soils of
the coastal plain, drink water from the Edwards
aquifer, enjoy the scenery of the Hill Country
(fig. 7), pump oil and gas from the subsurface,
play on the sandy Texas beaches of the Gulf
coast, and mine the limestone, volcanic rock, and
asphalt. Geologic processes continue. No more
earthquakes or volcanoes, but erosion continues,
and sediments continue being deposited.
Figure 7. Wildflowers along the road in Uvalde.
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GeoFORCE
Young Geoscientists
FIELD -TRIP STOPS
DAY 1
Where are we, what will we see?
Geographically, the Uvalde area is located
at the northern edge of the Gulf Coastal Plain
and the southern edge of the Edwards Plateau.
The rugged topography of the Edwards Plateau has canyons carved by rivers such as the
Nueces, Frio, and Leona. We will visit these
rivers during our trip. (Field-trip map)
Today you’ll learn about important
geological features,
• Volcanoes
• Depositional environments
• Karst
• Sedimentary rocks
• Igneous rocks
Geologic processes,
• Deposition and erosion
• Differential erosion
Uvalde area natural resources,
• Basalt
• Water resources, including rivers
and aquifers
Field-Trip Agenda
DAY 1
WELCOME BY SWTJC AND UT AUSTIN
O VERVIEW OF FIELD TRIP
Stop 1 Black Waterhole
Stop 2 Vulcan Knippa Traprock Quarry
Stop 3 Del Rio Formation
Stop 4 Mount Inge and Leona River
Stop 5 Bat Cave at Annandale Ranch
DAY 2
Stop 6 Vulcan Rock Asphalt Quarry
Stop 7 Big Oak River Camp and
Nueces River
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Today’s geo-words: At the end of the day,
you will be familiar with these terms:
River
Meander
Cutbank
Karst
Point bar
Watershed
Terrace
Aquifer
Groundwater
Water table
Magma
Basalt
Igneous rock
Columnar joints
Sedimentary rock
Quarry
Limestone
• Geologic processes
Deposition
Erosion
Differential erosion
Lithification
• Geologic Concept
Uniformitarianism
Geologic concepts,
• Uniformitarianism
• The Law of Superposition
and geoscience careers.
• Hydrogeology
• Paleontology
• Volcanology
• Planetary geology
Do you remember the Geologic Time Scale?
There’s one on the inside of the back cover of
the guidebook. The major divisions of geologic
time are
• Cenozoic Era (~ 65 million years ago
to present day).
• Mesozoic Era (~ 245 million years ago
to ~ 65 million years ago).
• Paleozoic Era (~ 545 million years ago
to ~ 245 million years ago).
• Precambrian (~ 545 million years ago
to the time of formation of the Earth
~4,600 million years ago).
Because so many of the rocks in this area
are Mesozoic in age, we’ve included a more
detailed geologic time scale of the Mesozoic
that will be a handy way for you to see when
important events in the Uvalde area occurred.
During our field trip, we will be referring
to the geologic time scale to learn about the
vastness of geologic time. The time scale has a
column for notes that you should use to mark
the ages of some of the geological features we
discuss on the field trip.
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STOP #1
• Wetland: An area of marsh or swamp
covered by water for long periods of
time. Wetlands help maintain water
quality by filtering out pollutants.
• River mouth: Where a river flows into
another river, a lake, or an ocean.
• Upstream: In the direction of the
headwaters.
• Downstream: In the direction of the
mouth of the river.
• Terrace: A deposit of sediment, usually
sands and gravels and finer sediments,
formed along the edges of a river by
floods. A terrace usually has a gently
sloping or almost flat surface. Terraces
are remnants of floodplains.
• Cutbank: The outside bank of a bend in
a stream or river, often eroding opposite
a point bar.
• Point bar: A low deposit of sediment
that forms along the inner bank of a
meandering stream.
Black Waterhole, Uvalde County, at the
Frio River and FM 1023 east of Uvalde (fig. 8)
Welcome to Black Waterhole and the Frio
River. This is a very interesting stop, where
we’ll learn about rivers and one of the many
ancient volcanoes located in the Uvalde area.
A river is a large natural stream of water. A
river system, or watershed, is an area drained by
a river and its tributaries. (Nueces River watershed map). Although not all rivers are alike, this
figure shows river systems similar to the ones
you will see on our field trip and rivers elsewhere around the world.
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OUR FIRST RIVER
OF THE TRIP
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Figure 8. An ancient volcano serves as the cutbank
on this part of the Frio River. The point bar in the
foreground is composed of gravel that was deposited
during the 2006 flood.
You are standing on the banks of the Frio
River. The Frio displays all of the parts of a
typical river. The Frio and all the rivers in the
Uvalde area are important sources of water
that are necessary for the survival of all living
things. Springs located in Real County are
the source of water for the Frio River (Nueces
River watershed map). The Frio is a tributary
of the Nueces River that flows into the Gulf of
Mexico. Later on in our trip we’ll visit the
Leona and Nueces Rivers.
The Frio River has been here a long time. The
drainage for the Frio formed 10 to 20 mil-lion
years ago during the Quaternary era. The river
has gone through great changes due to changes
in climate, periods of floods and drought,
and the effects of erosion and deposition.
Rivers are dynamic, and change is continuous.
Parts of a river system include
• Watershed: The area of land and water
where rain runs off into a particular
water system.
• Headwaters: The beginning of a river.
The source of the water may be a spring
or the runoff from rain or snow.
• Tributary: A smaller stream or river that
joins a larger stream or river.
• Floodplain: A flat land area on either side
of a river that can flood during heavy
rains. The floodplain is built from the
sediments deposited by the river.
• Meander: A curve or bend in the river
channel.
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the boulders were deposited. At the same time,
the cutbank was being eroded.
Most point bars are sand and other finer
sediments, not boulders. Why is there so little
sand in this point bar?
Figure 9 graph describes the amount of
energy needed to get sediments of different
sizes up into the water column (erosion) and to
keep them suspended to transport downstream.
Lowering the energy of the water column drops
sediment out of the water, and the sediment is
deposited.
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THE PRESENT
IS THE KEY TO
THE PAST
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Figure 9. Hjulstrom’s curve provides a description
of the amount of energy needed to get sediments
into the water column.
For instance, deposition and erosion are constant geologic processes that occur in rivers.
This part of the Frio is a good place to
observe deposition and erosion. The bend in the
river is a meander. The side of the meander
that is across the river from us is the river bank.
Water travels faster on that side of the river,
and sediment from the rock is eroded away
and deposited downstream. The side of the river
on which we are standing is called a point bar.
Water travels slower on this side of the river,
allowing the largest fragments to be deposited.
As the current slows even more, smaller-sized
sediment grains are deposited. The amount of
deposition and erosion depends on how fast
the water is flowing down the river. The size of
the rocks and sediment that are deposited on
the point bar depends on how fast the water is
flowing down the river. The heaviest rocks are
deposited first, and as the water flow continues
to slow down, the smaller rocks and sediment
are deposited (Nueces River watershed map). A
major flood in July 2002 deposited gravel and
other large pieces of rock at this point bar. Look
at the size of some of the boulders! Flowing water
is a powerful force, and the water was flowing
very fast to keep rocks this size moving down
the river. As the water slowed at this point bar,
A very important geologic concept called
Uniformitarianism means the present is the
key to the past. Modern processes that we see
today, such as erosion and deposition, were active in the distant geologic past, and they produced similar results. Long, long ago, water
flowed downhill, eroded rocks, carried sediments, and deposited them in ancient oceans,
rivers, and lakes, just as it does today. Sediments deposited in layers today could be layers
of rock in some geologic setting tomorrow.
Volcanoes! Black Waterhole is an interesting place on the Frio River because it gives
us an opportunity to observe another geologic
feature. It’s a volcano, and we are standing in
the middle of it!
So what is a volcano? A volcano is a place
where hot molten rock, gases, and water vapor
erupt from the interior of the Earth onto the
surface. Eruptions may be rather gentle or
violent explosions. The stuff that erupts from
a volcano may be fine particles of glassy ash,
hot flows of molten rock that ooze over the
landscape or roar out at high velocities, or
magma and rocks blasted from the throat of
the volcano. The shape of the volcano, whether
a tall steep-sided mountain or a low volcanic
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vent, depends on (1) the composition of the
material that’s erupted, (2) the character of the
eruption (gentle or violent), and (3) the length
of time the eruption continues.
Magma is hot molten rock; magma may
contain both fluids and some crystallized minerals. Igneous rocks are formed from magma
that has cooled and crystallized. When magma
cools, the chemicals in the magma crystallize
as minerals. The longer it takes to cool, the
more time the minerals have to develop, and
the larger the crystals in the resulting rock.
Minerals in igneous rocks that cooled slowly
in the subsurface are relatively coarse grained
and are called intrusive rocks. Minerals in volcanic rocks are generally fine grained because they
cooled quickly at or near the surface and are
called extrusive rocks. Lava is a flow of magma
that has erupted onto the Earth’s surface.
The volcanic rock at Black Waterhole is
basalt. It originated below the crust of the Earth
in the upper mantle, perhaps 25 miles (!) or more
beneath the surface. When you hold a piece of
basalt during the field trip, you are holding a
piece of the Earth’s upper mantle.
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Figure 10. A model of an undersea volcano very similar
to ancient volcanic conditions in the Uvalde area.
Eighty million years ago, much of Texas,
including the Uvalde area, was covered by a
warm, shallow ocean (fig. 5). Magma erupted
from volcanoes in the Uvalde area beneath the
shallow ocean water. As the magma approached the surface it came into contact with the
seawater, which caused powerful steam explosions. The explosive eruption excavated a deep
crater in the seafloor (fig. 10). Magma was
fragmented into volcanic ash, which blew high
into the air and fell back into a cone around
the central crater. The rock formed from the
ash is called tuff. The volcano later became a
subaerial (on the surface of the Earth) feature,
and magma erupted in dry conditions, forming
a lava lake inside the crater. The rock that was
formed from the lava flows is called basalt.
There are many ancient volcanoes in the
Uvalde area. Some are located in the subsurface,
but many can be seen at the surface. The
volcanoes in Uvalde were part of a chain of
active volcanoes called an igneous province that
extended from the Uvalde area and northeast
into Central Texas and continued into
Louisiana, Arkansas, Mississippi, Tennessee,
and Missouri (fig. 11).
Geoscience Question: What’s basalt,
and why is it important?
• Basalt is a very common volcanic rock
found in many places:
– Basalt is mined near Uvalde, Texas.
– The Hawaiian Islands are made
of basalt.
– Basalt is the main rock type on
the surface of the Moon.
• Basalt and plate tectonics:
– Basalt is erupted at the midocean
spreading centers.
– All the oceanic plates (oceanic crust)
are basalt.
• Basalts form from magmas that
originate in the Earth’s mantle.
• Basalt is a dark volcanic rock.
• Basalt magmas are extremely hot:
1,000 to 1,200o C.
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Figure 12. Knippa Traprock Quarry.
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A quarry is an open-pit mine where rock
or minerals are extracted to produce industrial
minerals such as aggregate (crushed rock) and
sand and gravel.
The Knippa Quarry is located in an ancient
volcano that is much larger than the volcano
at Black Waterhole (fig. 12). Both volcanoes
are in the Uvalde Igneous Province, and both
have the same type of volcanic rock, basalt. We
recognize these volcanic rocks as basalt because
they have the same mineral composition as
other volcanic rocks found in the Uvalde area,
and the same mineral composition as ancient
and modern basalts found elsewhere in the
world.
Look at a piece of the basalt you find at the
quarry. On the basis of what you have learned,
is it an intrusive or extrusive igneous rock?
The basalt in the Knippa Quarry shows a
feature common to many lava flows. As the lava
cooled and crystallized into rock, it began to
contract. Shrinkage of the rock mass resulted
in the development of numerous cracks, called
“joints.” This basalt cooled slowly near or on
the surface and formed a distinctive hexagonal
feature called columnar joints (fig. 13) that are a
common feature at this quarry.
The Knippa Quarry extracts the basalt,
also called traprock, that is used as ballast on
railroad tracks and for other construction
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Figure 11. Upper Cretaceous volcanic province in
Texas.
Factoid: CAMP DIX. Camp Dix, a
Confederate outpost established by James
M. Norris on April 4, 1862, was at the
crossing of the San Antonio–Eagle Pass
road and the Frio River, a spot on the river
known as Black Waterhole. The camp was a
Frontier Regiment post under the command
of Capt. John J. Dix, Jr. The road became
a vital commercial route to Mexico for the
Confederates when the Union forces gained
control of the entry points to Mexico along
the lower Rio Grande. Camp Dix was one of
several encampments established to protect
Confederate export wagon trains on their
way to Mexico. It was abandoned after the
consolidation of the Frontier Regiment
in March 1864 (from the Handbook of
Texas online at http://www.tsha.utexas.
edu/handbook/online/).
STOP #2
Knippa Traprock Quarry, owned and
operated by Vulcan Materials, Highway 90 in
Knippa, Texas
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Figure 13.
Volcanic rocks
such as basalt
contract as they
cool, forming
networks of
columnar joints
that divide the
rock into regular
polygonal
columns. This
is an example of
columnar joints
at the Knippa
Quarry.
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Figure 14. This paleogeographic map of what is now
the United States shows that a shallow sea covered
Texas during the Cretaceous.
purposes. The traprock produced in the Knippa
Quarry is used throughout Texas and in other
states. Many of the railroads in Texas have
tracks laid on crushed basalt from this area.
Basalt quarries are common in other parts of
the world.
Geoscience word. Traprock is a
mining name for a dense basaltic rock.
The term comes from the German word
“treppen” that means stairs, which refers
to the columnar joints common in many
basalts.
into rock is called lithification. The rock can
later be exposed at the surface by erosion of
the overlying rocks.
All sedimentary rocks offer clues to the
depositional environment in which the original sediments were deposited (fig. 14). Fossils
of coral and other animals that lived in the
sea indicate ocean conditions; mudcracks and
raindrop impressions tell us the area was
exposed at the surface; deposits of coal are evidence of ancient swamps. Beaches, reefs, river
channels, deltas, lagoons, and the deep sea
all have distinctive sedimentary deposits that
we can see in the rock record. “The present is
the key to the past.” When geoscientists look
at a sedimentary rock, one of the first things
they do is try to imagine the environment in
which the sediments were deposited. Knowing the sedimentary environment is important to geoscientists, who try to find natural
resources in sedimentary rocks.
STOP #3
Del Rio Formation, Hacienda Road, east
of Uvalde
We are standing on a geologic formation
called the Del Rio. This formation is a sedimentary rock that is found throughout Central
and South Texas. At this site, you will learn
how geoscientists interpret the environment in
which sedimentary rocks are formed.
How sedimentary rocks are formed.
Sediment that is deposited as a layer at the
surface of the Earth is commonly buried by
younger sediment that is deposited on top.
As the sediment is buried deeper into the
subsurface, it is exposed to heat, pressure, and
chemical changes. The sediment is compressed
by pressure, heat, and chemical changes and
forms rock. The process of turning sediments
The depositional environment
of the Del Rio Formation
Sediment that eventually formed into
the Del Rio Formation was deposited during
Cretaceous time around 100 million years ago.
• The sediment was deposited in an ocean
environment and was composed of
mostly silt and clay, with some shells
11
STOP #4
Mount Inge and Leona River, Uvalde,
junction of County Road 375 and RR 140
Another volcano! Mount Inge is the remains of an ancient volcano (fig. 16). Beneath
every volcano there is a volcanic vent that
allows the magma to ooze its way to the surface, where it may erupt as a volcano (fig. 10).
The magma at Mount Inge forced its way up
along cracks in the limestones. It may or may
not have made its way to the surface, where
it would have erupted as volcanic ash or lava
flows.
What happened to the limestones on
Mount Inge? They’ve eroded away. Why did
the limestones erode away and the basalt did
not? Basalt is more resistant to erosion than
limestone. Different types of rock erode at
different rates. Hard rocks are more resistant
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Figure 15. Fossils found in the Del Rio Formation are
evidence of a shallow ocean environment.
•
•
•
•
and shell fragments from oysters, clams,
and snails that lived in the ocean.
The silt and clay tell us that this was a
quiet-water environment. If there had
been lots of currents or waves, the silt
and clay would have been carried away.
The fossils tell us that it was shallow
water (fig. 15). These animals
live at depths only where the sunlight
can penetrate the water.
Erosion of overlying rocks exposed
the Del Rio at the surface.
Remnants of the abundant life
that lived in this shallow marine
environment are found in the
Del Rio rocks at this location.
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Figure 16. Mount Inge is an ancient volcano. Basalt
in the foreground has eroded from the volcano and
has been deposited at the base.
12
• The Leona, the Frio, and all the other
rivers that flow into the Nueces are part
of the Nueces River watershed.
Where would a grain of sand tossed into
the Leona River eventually be deposited?
The Uvalde area has an abundance of water
resources at the surface and in the subsurface
of the Earth.
• The Leona River’s source of water
(fig. 17) is a spring fed by a very
important aquifer called the Edwards.
• The Edwards aquifer provides water
to millions of people in Central and
South Texas from Austin to
San Antonio to Uvalde.
• Water found in subsurface rocks is called
groundwater. The subsurface rock where
the groundwater is located is called an
aquifer (fig. 18).
• Water from rain or rivers gets into the
aquifer by seeping through the soil and
rock above the aquifer; this process is
called recharge.
• The area of soil and rock above an
aquifer is called the recharge zone.
• Where the top of an aquifer, the water
table, intersects the surface of the Earth,
a spring is formed. Water leaves the
aquifer through springs, a process called
groundwater discharge.
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Figure 17. The Leona River is formed from springs
from the Edwards aquifer. Notice the cutbank and
point bar. What materials form the point bar?
than soft rocks. Soft rocks erode more easily
than hard rocks. The term we use to describe
rocks that erode at different rates is differential
erosion.
Mount Inge is located close to the Leona
River. The Leona has a lot of similarities to the
Frio River that we saw at Black Waterhole
(Nueces River watershed map). It is spring fed.
It is a tributary of the Frio River, which is a
tributary to the Nueces River, which flows to
the Gulf of Mexico.
• All the smaller streams that flow into
the Leona are part of the Leona River
watershed.
• The Leona and other rivers that flow
into the Frio River are part of the
Frio River watershed.
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��
Figure 18. Parts of an
aquifer system. The
Edwards aquifer is vital
to people and business in
South Texas, who count
on water for consumption,
industry, and recreation.
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13
A river, however, does not stay in exactly the
same channel. It changes its position by eroding sideways or downward. If it erodes sideways
it may erode one bank for many years, and then
the major flow and erosion may shift to the
other bank. As the river shifts sideways it may
partially or completely erode the floodplain.
As a stream erodes downward, it eventually
cuts a channel that is so deep that the old
floodplain is no longer commonly flooded.
What is left behind is a rather flat surface, a
terrace (fig. 19). A terrace is a fragment of old
floodplain deposits that is left behind as the
river erodes more deeply (fig. 20).
• Some terraces are ancient deposits
formed by rivers that are no longer
present, and others may be formed
along modern rivers.
• There are large areas of terrace deposits
in this part of Texas that formed a few
million years ago in the Quaternary Era,
when the climate was wetter and the
rivers were larger.
Factoid: The latest images from Mars
show distinct features that some scientists
interpret as evidence of ancient river systems
(fig. 21). Planetary geologists believe that this
image shows a former meandering stream that
was cut off as the channel adjusted its course.
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Figure 19. This view from Mount Inge shows a large
and ancient terrace where a river once flowed.
Rivers, floodplains and terraces:
Floodplains: When a river floods, the
waters rise to fill the channel and then spill
over the banks. If they are not confined in a
canyon, the floodwaters spread out over the
surrounding countryside. As the floodwaters
leave the channel, they slow down, and the
sediment carried by the water is deposited in a
flat sheet.
Over a long time and many floods, many
layers of sediment are deposited. A floodplain
is the area adjacent to a river that is commonly flooded; it typically is relatively flat.
Terraces: Once a major stream or river
is established, it may remain in about the
same general area for many thousands or even
millions of years. There is evidence that many
Texas rivers, for example, have been present in
the same general area for several million years.
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Figure 20. Parts of a terrace.
A terrace is a fragment of
old floodplain deposits that
is left behind as the river
erodes more deeply.
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14
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Bat Factoids: Most bats are nocturnal,
which means that they sleep during the day
and fly out at night to eat. Their main food
is insects. The baby and juvenile bats remain
in the cave until they are old enough to fly
and capture their own food. Bats navigate
using “echolocation,” which is somewhat
like radar. They send out very high pitched
sounds (through their noses!) and use their
sensitive ears to hear the echoes of the
returning sounds that bounce off things near
them, like insects, trees, and other bats. From
the echoes the bats quickly figure out the
direction and distance to these other things.
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Figure 21. Meandering channels provide evidence of
persistent flow of water through this area sometime
early in Martian history.
Bats live in geologic features called caves.
Most caves form in a sedimentary rock
called limestone. All day long, we have been
looking at rocks that formed in a shallow
marine environment. The sediments in this
depositional environment were formed mainly
of a fine lime mud composed of a mineral
called calcite (CaCO3). The calcite can form
directly from seawater or be formed by marine
plants and animals. Many of these creatures
are microscopic, but they also include larger
animals such as snails, clams, and oysters that
lived in the ocean. When these animals died,
their shells sank to the bottom of the ocean,
were buried by more sediment, and formed
limestone rock. After the limestone was raised
above sea level, groundwater, containing a weak
acid, dissolved the calcite in the limestone, and
caves were formed. Karst is the geologic term
for caves and holes in the limestone that has
been dissolved by groundwater.
STOP # 5
Annandale Ranch Bat Cave, County Road
127, Uvalde County, northeast of Uvalde
This evening we are going to witness
the flight of millions of bats that live in the
Annandale Bat Cave (fig. 22)! These free-tail
bats migrate between Mexico and Central and
South Texas every year. The bats migrate to
Latin America each fall and migrate back to
Texas in the spring. Experiencing the evening
flight of the bats is truly awesome.
What did we learn today?
River Systems
• A watershed is the area drained by a
river and its tributaries.
Volcanoes
• We saw examples of volcanic features
and learned about volcanic eruptions.
Figure 22. Annandale Ranch Bat Cave. The cave
was created when rainwater containing a weak acid
dissolved calcite found in the limestone. This process
takes thousands of years before a cave is formed.
15
• Tuff rock was formed from explosive
eruptions due to the interaction between
the magma and the ocean water.
• Basalt was formed from a more gentle
volcanic eruption where water and
magma did not mix.
• The characteristics of sediments
deposited in modern environments
(oceans, rivers, deserts) have the
same characteristics as sedimentary
rocks deposited in similar ancient
environments.
Differential erosion:
• Rocks erode differently depending
on their characteristics.
• Soft rocks erode more easily than
hard rocks.
Main divisions of geologic time:
• Cenozoic, Mesozoic, Paleozoic,
and Precambrian
• Cretaceous, Quaternary
Knippa Basalt Quarry
• The Uvalde area has many occurrences
of basalt.
• Basalt is mined for use as ballast beneath
train tracks, for road construction,
and for other purposes in Texas and
other states.
Sedimentary rocks are formed from sediments deposited on the Earth’s surface. The
sediments are lithified into rock by a combination of heat, pressure, and chemical changes
that occur after the sediments are buried by
younger deposits.
• All sedimentary rocks offer clues to the
depositional environment in which the
original sediments were deposited.
Water found in the subsurface is called
groundwater. The subsurface sediments and
rock where the groundwater is located are
called an aquifer.
Caves are commonly formed in limestone.
• Calcite in limestone is dissolved by acid
waters that flow through the rock and
form holes in the rock known as karst
or caves.
• Some bats live in large colonies in caves.
• Bats are nocturnal, which means they
sleep during the day and eat at night.
• Juvenile bats live in the cave until they
are ready to find their own food.
Uniformitarianism: The present is the key
to the past:
• Processes that are active today are the
same as those of the geologic past.
Why is what we learned important?
Water resources including rivers and aquifers are important natural resources in the
Uvalde area. Hydrogeologists study groundwater and aquifers. They are responsible for
determining the size of an aquifer, water-flow
properties, and water quality. They also work
with local authorities to manage this critical
natural resource to ensure that water is available for future generations.
Ancient volcanoes in the Uvalde area
provide an important natural resource called
basalt that is used for ballast for railroad tracks
and in road construction. Volcanologists study
the processes and deposits of volcanic eruptions to find out where, how, and when
volcanoes are likely to erupt. They work closely
with governmental agencies where volcanoes
are active to mitigate (reduce) the effects of
damage from volcanic activity. These volcanoes
are no longer active, but active volcanoes in
many places are a serious geohazard.
Geologists develop models to understand
depositional environments. Petroleum geologists use these models to find oil and natural
16
gas in sedimentary rocks. Paleontologists study
the changes and distribution of life on Earth
in time and space and use fossils to date the
age of rocks. Sedimentologists study the nature, origin, distribution, and alteration of
sediments, such as sand, silt, and mud. Oil,
gas, coal, and many mineral deposits occur in
such sediments. Planetary geologists use their
knowledge of geologic processes on Earth to
study geologic processes on other planets.
Planetary geologists look for evidence of
water, one of the necessary components for
life, on other planets.
It is important for people building houses or
roads to know where the Del Rio clay is located.
Because the clay is not very stable, foundations
built on the clay often crack, and roads need
more maintenance. How do they know where
the Del Rio is present? They ask a geologist.
• Geologic concepts
Law of Superposition
STOP # 6 :
Rock Asphalt Quarry, operated by
Vulcan Materials, Intersection of Highway 90
and 1022, about 15 miles west of Uvalde
(fig. 23)
We are at the site of another important
quarry in the Uvalde area. It is also owned and
operated by Vulcan Materials, a major mining
company in the United States. Staff that work
at the mine will be our tour guides and will
teach us about the operations of an asphalt
mine. The mine is located in the Asphalt Belt
of Uvalde County (field-trip map). The mine
produces a product that is a mixture of crushed
limestone and asphalt that is used to pave
roads in many parts of Texas; a similar product
is used for roofing and waterproofing.
What is asphalt? Asphalt is the gooey,
tarry, dark-brown to black stuff that is made
from crude oil. It can be made in an oil refinery,
or it can occur naturally. If crude oil is heated,
many of the hydrocarbons that make it flow
easily are evaporated. The remaining material
flows very slowly or is a solid. You’ve all seen asphalt. Most of our highways are paved with it.
Day 2
What will we see and learn?
Today we are going to visit another quarry
in the Uvalde area that produces asphalt, an
important natural resource that is used in
road construction.
A reservoir is a subsurface body of rock
having sufficient porosity and permeability to
store and transmit fluids that include water,
crude oil, and natural gas. Limestone is an
important reservoir for petroleum.
We will learn the geologic concept called
the Law of Superposition, in which younger
rocks are deposited above older rocks.
Our final stop of the field trip will be at
the Nueces River, the major river in the
Uvalde area.
Today’s geo-words: At the end of the day,
you should be able to define these terms:
• Uvalde-area natural resources
Asphalt
Figure 23.
Vulcan
Rock
Asphalt
Quarry.
17
• Composed of coarse grains of shell and
limestone fragments that were deposited
in a high-energy shallow ocean
environment with moving water,
waves, and currents.
• Fossils such as mollusk fragments,
algae (one-celled plants that serve as
food for aquatic animals) and forams
(microorganisms having calcareous
shells) that are also clues of an ocean
environment.
What are the similarities and the differences between the Anacacho and Del Rio
depositional environments?
The Law of Superposition is an important
concept that geologists use to understand the
sequence of rock formations. As you stand in
the quarry, look at the walls of rock. Some of
them are quite broken up, but on others you
can see the layers, the “bedding,” of the limestone.
• Sedimentary rocks are formed from
layers of sediments, and the layers
were deposited in a sequence.
• Each new layer is deposited on the
older layer beneath it.
• In a stack of sedimentary layers,
the oldest is on the bottom and the
youngest is at the top (fig. 24).
This is a simple concept, the idea that
younger layers are on top of older layers, but
the Law of Superposition is very important
in interpreting the sequences of events that
form sedimentary rocks (fig. 25).
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Figure 24. Asphalt-bearing Anacacho Formation.
The Law of Superposition states that younger
rocks overlie older rocks.
Asphalt at the quarry occurs in the Cretaceous Anacacho limestone.
There are two theories about how the
asphalt formed:
1. The crude oil was trapped in subsurface
rocks called reservoirs. A trap is a barrier
to the upward migration of petroleum
that allows it to accumulate in a
reservoir. When the trap was no longer
available to hold the oil, it escaped from
the reservoir, and gravity forced the oil
upward toward the surface. The oil was
deposited close to the surface in the
Anacacho limestone and hardened
into asphalt.
2. Magma associated with local volcanic
activity may have driven the oil into
the porous Anacacho limestone.
The Anacacho asphalt-bearing limestone
units are:
Figure 25. Diagram showing
the Law of Superposition.
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18
Factoid: For the past 2 days, we have
been learning about the geologic processes
and natural resources that are formed in the
Earth’s crust. What about geology that is
out of this world? In the 1980’s, geologists
found evidence of a meteorite impact site
just south of Uvalde. The impact occurred
approximately 40 million years ago and is
1.5 miles in diameter.
Factoid: If crude oil remains trapped
in a reservoir, it becomes a valuable natural
resource that we can refine to make fuels
that we use every day in our cars, boats,
and airplanes. Crude oil is a finite natural
resource. When this resource becomes
depleted, it will no longer be available as a
form of energy for humans to use. There is
much controversy surrounding how much
oil will be available to us in the future.
Why is what we saw today important?
The Uvalde area is rich in asphalt deposits.
Mining engineers manage the construction
and operations of a mine that are crucial in
developing a successful mine.
The Nueces River is a major watershed for
South Texas. The Nueces provides a source of
water to many people from Uvalde all the way
to the Gulf coast. Hydrologists study the occurrence, movement, and properties of water
on the Earth’s surface and in the subsurface.
They solve problems associated with floods and
water pollution. Hydrologists play a major
role in managing the potential impacts associated with human interaction with rivers, wetlands, and aquifers.
STOP #7:
Big Oak River Camp and Nueces River
Highway 55, Camp Wood, Texas
We’ve made it to our last stop. We’re
standing in the floodplain of the Nueces River.
The Nueces is the largest river in the Uvalde
area. The Leona and Frio Rivers are tributaries
of the Nueces. The Nueces River watershed is
the major watershed for the area from Real
County to Corpus Christi, some 400 miles,
where the water from the Nueces discharges into
the Gulf of Mexico (Nueces River watershed
map).
You will notice features on the Nueces that
are very similar to geologic features at the Frio
and Leona Rivers (Figs. 26 and 27). Can you
identify these features?
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Figures 26 and 27. The two sides of the Nueces River at Big Oak River Camp in Camp Wood.
Which figure represents the cutbank and which represents the point bar and why?
19
fossil, drive by an ancient volcano, or drive
on a bridge over one of the local rivers, you
will understand the processes behind these
geologic features better than most other
people. This knowledge is very powerful.
You did it! Congratulations!
THAT’S THE TRIP:
You have learned a great deal about the
geology in your backyard of Uvalde. We hope
that the field trip has opened up a new world
of discovery for you. The next time you see a
Figure 28. 2006 Young Geoscientists. They did it!
A Final Thanks:
Much of the inspiration for this guidebook came from the 2004 South Texas Geological Society publication Volcanoes, Asphalt,
Tectonics and Groundwater in the Uvalde
Area, Southwest Texas: Field Trip Guidebook,
written by Dr. Thomas E. Ewing. Volcanic Features of the Austin Area, Texas, by S. Christopher
Caran, Todd Housh, and Alan J. Cherepon
of the Austin Geological Society, was another
very useful reference.
The authors of this guidebook are Sigrid
Clift and Jay Raney. Sigrid is a geologist at the
Bureau of Economic Geology, a major research
unit of the John A. and Katherine G. Jackson
School of Geosciences at The University of
Texas at Austin. Jay recently retired from the
Bureau of Economic Geology and is now living
in Salem, Oregon.
20
Figure
Acknowledgments
The guidebook was suggested and made
possible by the Jackson School of Geosciences and the sponsors of GeoFORCE.
Doug Ratcliff and Julie Spink provided consultation, guidance, and constant support.
Dr. Julie Jackson, formerly at The University
of Texas at Austin and now at Texas State
University, is our educational mentor. She
develops the tests and quizzes and provides
insightful comments on how best to present
our science. At the Bureau of Economic Geology’s Media Technologies Group, Joel Lardon,
Jamie Coggin, and John Ames prepared the
graphics and the layout of the guidebook.
Susie Doenges and Lana Dieterich added greatly
to the clarity of our text. All are a pleasure to
work with.
This guidebook is a noncommercial, informal educational product for the limited use of
the GeoFORCE Program. Most figures were
either prepared by the Bureau of Economic
Geology or are from noncommercial sources
that allow free use for educational purposes.
A few figures are either of uncertain heritages
or are from sources on the Web that we have
not yet determined whether they allow broader
utilization and distribution.
The following figures were derived from the
people, organizations, and sources acknowledged below. All other images and graphics
were developed by the authors of the guidebook
and the staff at the Jackson School of Geosciences.
Figure 4: Smithsonian National Museum of
American History, http://www.si.edu/
Figure 9: Dr. Steve Ratchford, University of the
Virgin Islands, http://faculty.uvi.edu/users/sratchf/
SSEA_ocean/files/sediments/sediments03.htm
Figure 10: 2006, S. Christopher Caran,
Volcanic Features of the Austin Area, Texas,
Austin Geological Society
Figure 21: David E. Trilling, University of
Pennsylvania, http://alpaca.as.arizona.edu/~trilling/
teaching/spring2004/lectures/lecture19/s76.html
Nueces River Watershed diagram: Modified from
2002 Nueces River Basin Regional Water
Supply Planning Study by U.S. Army Corps
of Engineers and HDR Engineering,
http://www.swf.usace.army.mil/pubdata/notices/
nueces/Report_pgs_1-10.pdf
21
Geo-Glossary
Aquifer:
A body of rock in the subsurface
in which all the spaces in the
rock are filled with water; the
rock must have enough open spaces
that a water well in the rock can
be used to produce useful
quantities of water.
Asphalt:
A dark-brown to black, almost
solid, hydrocarbon produced
from the residue left after the
distillation of crude oil. Asphalt
is used on roofs and highways
as a waterproofing agent.
Ballast:
Broken stone and gravel used
to add weight and durability.
Basalt quarried in Knippa is
used as the base for railroad tracks
and provides track stability,
drainage, and support of heavy
loads carried by railcars.
Basalt:
A dark volcanic rock composed
chiefly of calcium-rich feldspar
and iron- and magnesium-rich
minerals. There is not enough silica
in the magma to form the silicarich mineral quartz.
Calcite:
Mineral composed of calcium
carbonate (CaCO3).
Cave:
An underground opening with
access from the surface of the
ground or from the sea.
Cenozoic:
The geologic period dating from
65 millions years ago through the
present. Cenozoic is Greek for
“new era.”
Columnar joints:
Volcanic rocks such as basalt
contract as they cool, forming
networks of columnar joints
that divide the rock into regular
polygonal columns.
Crater:
A depression; it may be produced
by a meteorite impact or a
volcanic eruption.
Cretaceous:
The geologic period dating from
135 million years ago to 65 million
years ago.
Cross section:
Shows geologic features as they
would appear on a vertical plane.
Crude oil:
Unrefined liquid petroleum.
It ranges in density from very light
to very heavy and from yellow
to black in color. It may contain
paraffin and asphalt.
Cutbank:
The outside bank of a bend in
a stream or river, often eroding
opposite a point bar.
Deposition:
The process of formation of a
deposit of sediments. It may occur
as a chemical precipitate or as a
result of the sedimentary particles
dropping out of a fluid (water or
air) as a result of reduced velocity.
Depositional
environment:
The conditions under which
sediments were laid down.
Depositional environments are
divided into four groups: marine
(ocean), eolian (wind), alluvial
(rivers), and deltaic (delta).
Differential erosion: Occurs because some rocks or
soils have characteristics that make
them erode more or less easily
compared with adjacent rocks and
soils. Rock that is more resistant
to erosion forms steeper slopes or
cliffs relative to an adjacent rock
that erodes more easily and forms
gentler slopes. (See erosion.)
Discharge:
22
The process by which water
in the subsurface of the Earth
(groundwater) moves to the
surface. Discharge occurs in seeps
or springs, but it may also occur
in lakes, rivers, or oceans (See
recharge). Discharge is also used
to describe the volume of water
flowing in a river or stream; usually
measured in cubic feet per second.
Downstream:
In the direction with the flow of a
stream or river; toward the mouth
of a river.
Erosion:
The process of wearing down
the surface of the Earth. Physical
erosion by flowing water, rain,
wind, or ice is an example of
common erosional processes.
Chemical erosion, such as slightly
acid rainwater causing the chemical
breakdown of limestone, is also an
important erosional process.
Extrusive rock:
An igneous rock formed from
lava that has flowed out onto the
Earth’s surface, characterized by
rapid solidification and grains that
are so small as to be barely visible
to the naked eye.
Floodplain:
Formation:
Fossil:
Geologic time
scale:
Groundwater:
Water in rocks or soils below the
surface of the Earth. (See aquifer.)
Headwater:
The beginning of a river. The
source of the water may be a spring
or the runoff from rain or snow.
Hydrocarbons:
Include fossil fuels such as crude
oil, natural gas, coal, lignite, and
asphalt.
Hydrogeologists:
Scientists who study surface water,
groundwater, and aquifers. They
are responsible for determining
the size of an aquifer, water flow
properties, and water quality.
They also work with local
authorities to manage this critical
natural resource to ensure that
water is available for future
generations and investigate
waters at contaminated sites.
Hydrology:
The study of water. Hydrologists
are scientists who study water;
this is a somewhat more general
term than “hydrogeologist.”
Igneous province: A large area in which extrusive
and intrusive rocks occur.
The area adjacent to a river that is
commonly flooded; it typically is
relatively flat.
Igneous rock:
Rock that is formed from magma
that has cooled and crystallized.
Intrusive rock:
Rock formed by the cooling and
solidification of magma beneath
the Earth’s surface.
The remains or other evidence
(such as an impression) of a plant
or animal that is preserved in
the rocks or soils of the Earth.
(See paleontology.)
Karst:
Caves and other landforms are
formed in areas where solution
processes, rather than mechanical
erosion processes, predominate.
Karst is most often seen in
limestone.
A table used by geologists and
other scientists to describe the
timing and relationships between
events that have occurred during
the history of the Earth.
Lava:
A flow of magma that has
erupted onto the Earth’s surface.
(See magma.)
Name given to a rock unit that has
generally the same characteristics
over a large area. An example is the
Del Rio Formation.
23
Law of
Superposition:
Limestone:
Lithification:
In a sequence of sedimentary rocks,
the lowest layers are the oldest,
and the uppermost layers are the
youngest.
A chemical sedimentary rock
composed of the mineral calcite
(calcium carbonate). The primary
source of this calcite is marine
organisms.
Hot molten rock. (See lava.)
Meander:
To wander in no specific direction.
A river channel that curves and
bends is described as meandering.
Meander bends typically develop
on low-gradient rivers.
Metamorphic:
Planetary geologist: Scientist who study geologic
processes on other planets.
The process of turning sediments
into rock.
Magma:
Mesozoic:
Petroleum geologist:
People trained to search for and
find oil and natural gas. They
gather data to interpret reservoir
properties and recommend
locations for the wells.
The geologic period from 245 to
65 million years ago. Mesozoic
is Greek for “middle era.”
Rocks that have been altered
by heat, pressure, or changes
in composition.
Mining engineers: People trained to manage the
construction and operation
of a mining operation.
Mining geologists: People trained in geology to
characterize deposits of useful
rocks and minerals for the purpose
of mining these resources.
Paleontologist:
Paleozoic:
Earth scientists who deal with the
classification and distribution of
fossils in time and space and the
interpretation of the development
of life forms. (See fossil.)
The geologic period from 545 to
245 million years ago. Paleozoic
is Greek for “old era.”
24
Point bar:
A low deposit of sediment that
forms along the inner bank of a
meandering stream.
Precambrian:
The geologic period from
545 million years ago to the time
of the formation of the Earth at
4,600 million years ago.
Quarry:
An open-pit mine where rock
or minerals are extracted to
produce industrial minerals such
as aggregate (crushed rock) and
sand and gravel.
Quaternary:
The youngest period in the
Cenozoic Era that includes
the present through 2 million
years ago.
Recharge:
The process by which water moves
from the surface of the Earth
(surface water) into the subsurface
(groundwater). It can be rapid,
through caves or large fractures, or
very slow through the tiny pores in
the soils and rocks. (See discharge.)
Reservoir:
A rock formation or “trap”
containing oil, natural gas,
or water.
River mouth:
Where a river empties into the
sea or another body of water.
Rock:
A natural substance composed
of one or more minerals.
Sediment:
The loose pieces of rock that are
the result of erosion and
weathering; also the chemical
deposits precipitated from water.
Sedimentary rock: Rock composed of sediments
that have been lithified.
(See lithification.)
Sedimentologist:
Scientist who study sediment.
Spring:
A place where groundwater is
discharged from a rock or the soil
onto the land surface or into a
body of surface water.
Stratigraphy:
Branch of geology concerned
with the arrangement of layered
sedimentary rocks. (See Law of
Superposition.)
Subaerial:
Occurring on land or at the Earth’s
surface, as opposed to underwater
or underground.
Superposition:
In a sequence of sedimentary
layers, the overlying layer is
younger than the layer beneath it.
Terrace:
A fragment of the floodplain that
is left behind as the river erodes
more deeply. A terrace is typically
quite flat and has low relief.
Trap:
A structure that prevents the
upward or lateral movement
of liquids out of a subsurface
reservoir. Liquids can include
water, oil, and natural gas.
Traprock:
A mining name for a hard rock
used as aggregate; commonly
produced from basalt. The name
comes from the German word
treppen, meaning stairs.
Tributary:
A smaller river or stream that flows
into a larger river or stream.
Tuff:
Term used for volcanic ash that has
been consolidated and cemented.
Uniformitarianism: A term for the concept that the
“present is the key to the past.”
The main idea is that present-day
processes act in the same way and
at about the same rate as processes
have acted in past geologic times
and produce similar results.
25
Upstream:
Toward the source of a river or
stream and against the current.
Volcanic ash:
Pieces of volcanic rock that
is exploded from a vent into
fragments less than 2 millimeters
in size. Ash may be solid or
molten when first erupted.
Volcano:
A place where hot molten rock,
gases, and water vapor erupt
from the interior of the Earth
onto the surface.
Volcanologists:
Scientists who study volcanoes.
Watershed:
A drainage basin. All the surface
water in a watershed flows
(or “drains”) to a single river or
other body of water.
Water table:
The surface between where the
pore space in rock is filled with
water and where the pore space
in rock is filled with air.
Wetlands:
An area of marsh or swamp
covered by water for long periods
of time. Wetlands help maintain
Field-Trip Route
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28
The Quiz Assistant
STOP 2
Questions
1. What is columnar jointing?
Einstein
Terms
– Quarry
Einstein wants to help you learn the
important topics and terms that you should
know at the end of your field trip, so he has
compiled a list of questions and terms that
will be on the quiz. All you have to do is
go to the stop where a particular subject
was discussed and find the answer. If you
use Einstein’s quiz assistant, you are sure to
do well!
STOP 3
Questions
1. What important clues do sedimentary
rocks tell geologists about how the
original sediments were deposited?
Terms
– Lithification
STOP 1
STOP 4
Questions
1. What is basalt and why is it important?
2. How is igneous rock formed?
3. What is formed by the deposition of
sediments along the inner bank of a
meandering stream?
4. What is formed when the outside bank
of a bend in a stream or river is eroded?
5. What determines the size of rock and
sediment that are deposited on a point
bar?
6. What does the geologic concept
uniformitarianism state?
Questions
1. Groundwater, recharge, discharge,
water table, and springs are part of
what important water resource?
2. What is the description of a terrace?
3. What is the term we use to describe the
different rates at which rock erodes?
4. What is an area drained by a river called?
STOP 5
Terms
– Volcano
– Magma
– River
Questions
1. What is the term for caves and holes
in limestone that have been dissolved
by groundwater?
Terms
– Limestone
29
The Quiz Assistant
These are questions that you will
find throughout the guidebook.
(Hint. You’ll find all of this
information on pages 1, 4, 16, and 17)
Einstein
1. What are the crucial roles that
geoscientists play?
2. What term describes oil, natural gas,
coal, lignite, and asphalt?
3. What is the study of groundwater and
aquifers called?
4. What is the study of the geology of
other planets called?
5. What do we call a geologist that finds
oil and natural gas?
STOP 6
Questions
1. What is a gooey, tarry, dark-brown to
black substance made from crude oil
called?
2. What does the Law of
Superposition state?
Terms
– Superposition
30