COUNTY COMMISSIONERS
John Hutchings
District One
Gary Edwards
District Two
Bud Blake
District Three
RESOURCE STEWARDSHIP DEPARTMENT
Creating Solutions for Our Future
Brent A. Butler, AICP, Director
April 28, 2017
Thurston County Mineral Resource Lands
Aggregate & Quarry Rock Classification System
Thurston County is currently reviewing a county-wide inventory and classification scheme of
mineral resource lands. Mineral resource lands are areas where geology and other factors may
support the commercial extraction of minerals, including sand, gravel, rock, and metals.
The materials under review include a table and a map.
Table 1 (next page) displays the draft classification scheme, which is divided into two parts:

The upper half of the table shows the classification system for sand and gravel
(aggregate) with resource quality decreasing to the right and resource quantity (thickness
or volume) decreasing downward. The highest quality and quantity aggregate is classified
as A1 (upper left box) and the lowest quantity and quality aggregate is classified as C3
(lower right box).

The lower part of the table classifies quarry rock by quality only (types A1, B1, and C1).
Type 2 and 3 (types B2, B3, C2 and C3) bedrock resource units are undivided bedrock
formations that may have long-term commercial significance.

Non-resource is classified as D for both aggregate and quarry rock.
The County-wide map displays draft locations and classifications of potential mineral resources
In addition to the classification scheme listed in the table, the map includes geologic unit
abbreviations, which provide the time and lithology of various mapped geologic formations.
 Quaternary glacial outwash (unit Qgo)
 Quaternary glacial outwash, Vashon advance outwash (unit Qga)
 Eocene volcanic rocks of the Crescent Formation (unit Evc)
For further information on the geologic mapping of Thurston County and geologic unit naming
conventions, visit the Washington State Department of Natural Resources, Division of Geology
and Earth Resources website at http://www.dnr.wa.gov/programs-and-services/geology/geologicmaps.
2000 Lakeridge Drive SW, Olympia, Washington 98502 (360) 786-5490/FAX (360) 754-2939
TDD (360) 754-2933
Website: www.co.thurston.wa.us/permitting
Table 1. Thurston County Mineral Resource Lands Aggregate Quarry Rock Classification System
Sand and Gravel
(Aggregate)
Resource Strata
decreasing resource quality
Type 211
Type
311
Quality Type B13
25percent fines5
• Up to
• 70:30 to 30:70 sand and gravel ratio
• >25 years’ life expectancy
• Minimum 240,000 yd3/acre
• >100 feet thick
• Minimum overburden
• Up to 25 percent fines
• 70:30 to 30:70 sand and gravel ratio
• 10 to 25 years’ life expectancy
• Average 80,000 to 240,000 yd3/acre
• 50 to 100 feet thick
• Overburden <15 feet thick
• Up to 25 percent fines
• 70:30 to 30:70 sand and gravel ratio
• Life expectancy variable, generally <10 years
• Average 15,000 to 80,000 yd3/ acre
• Thickness varies, typically <50 feet
Quality Type C7
Quality Type D4
• Generally
unsuitable for
extraction
• >25 percent
fines5, may have
high organic
content
• Out of 70:30 to
30:70 sand and
gravel range
• No life expectancy
• <15,000 yd3/acre
• Limited depth
Quality Type D8
• Formation generally well mapped and (or) high
percentage of formation contains resource
strata of type A
• Meets or exceeds WSDOT specs for all rock
products
• Minimal amount of fractures9
• Minimal percent waste rock
• 20 percent or more rockery- size material produced
• Formation mostly divided locally and contains a
high percentage of resource strata of type B
• Meets WSDOT specs for some rock products
• Fractures vary from minor to very prevalent9
• Up to 10 percent waste rock
• 20 percent or less rockery-size material
produced10
None
• Formation undivided12 and >50% of formation
contains mostly resource strata of type B as
defined for Type 1 bedrock
• Formation mostly divided locally and contains • Generally
a high percentage of resource strata of type C unsuitable for
extraction8
• Rock will not meet WSDOT specs
• >30 percent waste
• Highly fractured9
rock
• 10 to 30 percent waste rock
• Highly to very highly
• Minimal rockery-size material produced10
fractured9 and (or)
weathered and (or)
poorly lithified
• No rockery• Formation undivided12 and >50% of
formation contains mostly resource strata of size material
produced
type C as defined for Type 1 bedrock
• Formation undivided12 and <50% formation
contains mostly resource strata of type B as
defined for Type 1
• Formation undivided12 and <50% of
formation contains mostly resource strata of
type C as defined for Type 1
R
Decreasing interbedded resource strata
Quality Type A
• Up to 15
• 70:30 to 30:70 sand and gravel ratio
• >25 years’ life expectancy
• Minimum 240,000 yd3/acre
• >100 feet thick
• Minimum overburden
• Up to 15 percent fines
• 70:30 to 30:70 sand and gravel ratio
• 10 to 25 years’ life expectancy
• Average 80,000 to 240,000 yd3/acre
• 50 to 100 feet thick
• Overburden <15 feet thick
• Up to 15 percent fines
• 70:30 to 30:70 sand and gravel ratio
• Life expectancy variable, generally <10 years
• Average 15,000 to •80,000 yd3/acre
• Thickness varies, typically <50 feet
AF
• <5
• 70:30 to 30:70 sand and gravel ratio
Quantity • >25 years’ life expectancy
Type 1 • Minimum 240,000 yd3/acre
• >100 feet thick
• Minimum overburden
• <5 percent fines
• 70:30 to 30:70 sand and gravel ratio
Quantity • 10 to 25 years’ life expectancy
Type 2
• Average 80,000 to 240,000 yd3/acre
• 50 to I00 feet thick
• Overburden <15 feet thick
• <5 percent fines
• 70:30 to 30:70 sand and gravel ratio
Quantity • Life expectancy variable, generally <10 years
Type 3
• Average 15,000 to 80,000 yd3/acre
• Thickness varies, typically <50 feet
percent fines5
Quality Type C3
T
percent fines5
Quarry Rock6
(Bedrock)
NonResource
Quality Type B2
D
Decreasing resource thickness and volume
Quality Type A1
Type 110
April 21, 2017
1 Type A sand and gravel is generally suitable for use in concrete. Aggregate meets or exceeds WSDOT specs for all products.
2 Because of variability of grain size and fines content, Type B sand and gravel is less likely to be utilized in concrete and is generally considered to be a borrow source. Aggregate meets WSDOT specs for most or all products.
3 Type C sand and gravel is highly variable in grain size, generally sound, and is suitable for roadway fill and small borrow pits; not suitable for concrete. Aggregate is near or below WSDOT specs for most or all
products.
4 Type D deposits may include fine sand, silt, clay, or lodgement till.
5 Fines are defined as percent material passing through a No. 200 sieve size.
6 The depth of the bedrock is immense, and essentially incalculable in the scope of this study. Mining depth would be limited by quality and other land use and environmental constraints. Hence, bedrock has been
classified by quality considerations only at this time.
R
AF
T
Type C bedrock may break down easily due to the previous effects of hypothermic activity, metamorphism, or weathering.
Type D bedrock may mostly include poorly quality sedimentary and volcanic rock.
Fracture pattern in bedrock deposits may vary depending on other quality factors.
Type 1 bedrock resources are typically compound lava flows or igneous intrusions that contain abundant Type A and/or B igneous rock types.
Type 2 and 3 resource units are undivided bedrock formations and thus constituent interstratified resource strata (e.g., Type A or B lava flows) are not currently subdivided (mapped) within the formation.
Type 1 strata locally mapped within Type 2 and 3 resource units within undivided bedrock formations determined using mine, LiDAR, previous small study geologic mapping, and other sources.
The Skookumchuck Formation and Puget Group (Type B3) generally lack quarry rock resource strata but contain local silica sand and clay in sedimentary interbeds of arkosic sandstone and claystone, respectively.
D
7
8
9
10
11
12
13