California’s deserts: produced by
mid-latitude
id l i d andd rain
i shadow
h d
Death Valley
Wi
d
d Sl
Windward
Slopes
• Windward surface is
compact
• Upper
U
part off the
h ddune
right before the crest is
where accretion sand is
(the most compact sand).
• The surface is marked by
little ripples.
ripples
• Angle of the slope is 10 to
g
15 degrees.
L ffacing
Lee
i slopes.
l
• lee facing slope is
where most deposition
of sand occurs.
• Angle of repose is 34
degrees.
• Any greater angle
produces
d
avalanches.
l h
Linear dunes of ferruginous sands,
Si
Simpson
Desert,
D
Australia
A
li
66-99 feet high, up to 60 miles long
Windward & leeward slopes
Transverse dunes
Whi h is
Which
i the
th leeward
l
d face?
f ?
Barchans migrating in clusters
Barchans,
Transverse dunes
A desert playa lake, Death Valley, California
Evaporite minerals
Source of evaporite minerals such as borax, and bad water because of high alkalinity or salinity
Mojave Desert
Colorado Desert
Desert Pavement
Rock varnish:
clay + Mn & Fe oxides
Ventifact: A sand
sand-blasted
blasted polished rock
P
Petroglyphs
l h by
b early
l native
i Americans
A
i
Newspaper Rock, Canyonlands, Utah
Pleistocene Lake Manix
Throughout the region during the late Pleistocene,
precipitation was perhaps 40 percent greater than present,
present
while temperatures were substantially cooler, especially at
higher elevations where year-round accumulations of ice and
snow existed.
Pleistocene Lake Manix
• Water from Mojave River (which drains the high desert and
Transverse Range to the south).
• Total depth
p reached 200 feet
• Four lake fillings are recognized. Sequential shorelines left by
Lake Manix are present at the 1880', 1840', 1800' and 1780'
elevations.
l
i
Lake Manix and Afton Canyon
Lake Manix
Afton Canyon
Viewed from the Calico Hills, Lake Manix is the white
band just below the distant horizon.
The 1780 ft. shoreline of Pleistocene Lake Manix.
Mojave River
This tributary has incised in response to the rapidly lowered base
level of Afton Canyon.
Kelso Dunes
Lake Manix
Afton Canyon
Kelso Dunes
O i i off the
Origins
h sand
d
• Soda Dry Lake to the
north.
• Afton Canyon to the
west.
To Afton Canyon
Kelso Dunes
• Most sand came from Afton Canyon
• Mineral composition
• Sand grain shapes
G it Mountains
Granite
M
t i
• Highly weathered
• Source
S
off sand
d
ZZYZX (dry Soda Lake)
•Lodgings/food
•Oasis
O i
•Dry Lake Bed
Wind Blows in All Directions
Circles in the sand
• The wind blows in all
directions
• Plant leaves in contact
with the sand create
crescents andd circles
i l in
i
the sand.
D
Dune
F
Formations
ti
Mitchell Caverns
The rocks are mostly Paleozoic limestone.
Mitchell Caverns
Bird Spring Formation
• Pennsylvanian
P
l i andd Permian
P
i (250-300
(250 300 myo)) limestone
li
t
• Bits of brown chert (from volcanic ash in the limestone
• Contain fossils Brachiopods, fusulinids, crinoids +
Cracks
C
k in
i the
h limestone
li
fill with
i h rain
i
+ CO2 (during wet times that
formed Lake Manix))
CO2 dissolves
limestone
After the ice age (10,000 years ago)
water table dropped, leaving caves
b hi d
behind
The lighted interior of Mitchell
Caverns.
Caverns
Stalactites.
Stalagmites.