215—Altamont-Sehorn complex, 15 to 30 percent slopes
Map Unit Setting
General location:
Lower Coast Range foothills on steep ridges
MLRA:
15
Mapunit geomorphic
setting: Hill
Elevation:
200 to 800 feet (61 to 244 meters)
Mean annual precipitation:
14 to 18 inches (355 to 458 millimeters)
Mean annual air temperature:
61 to 63 degrees F. (16 to 17 degrees C.)
Frost-free period:
225 to 250 days
Altamont silty clay—45
percent
Sehorn silty clay—35 percent
Minor components:
20 percent
Major Component Description
Altamont silty clay
Component geomorphic setting:
Lower sideslopes and north slopes of hill
Parent material:
Residuum weathered from sandstone-shale
Typical vegetation:
Annual grasses with scattered blue oak
Component Properties and Qualities
Slope:
15 to 30 percent
Runoff:
Medium
Surface features:
Polygonal cracking pattern, approximately 24 inches in diameter.
Percent area covered by surface
coarse fragments: None noted.
Depth to restrictive feature:
Bedrock (paralithic)—40 to 60 inches
Slowest permeability class:
Slow above the bedrock
Salinity:
Not saline
Sodicity:
Not sodic
Available water capacity:
About 7.9 inches (High)
Component Hydrologic Properties
Present flooding:
None
Present ponding:
None
Current water table:
None noted.
Natural drainage class:
Well drained
Interpretive Groups
Land capability irrigated:
Not calculated
Land capability nonirrigated: 4e-5
Typical Profile
A—0 to 3 inches; silty clay
Bw—3 to 9 inches; silty clay
Bss1—9 to 23 inches; silty
clay
Bss2—23 to 35 inches; silty
clay
BC1—35 to 43 inches; very
gravelly silty clay
BC2—43 to 49 inches; silty
clay
Cr—49 inches; soft or
weathered bedrock
Sehorn silty clay
Component geomorphic setting:
Sideslopes on hill
Parent material:
Residuum weathered from sandstone-shale
Typical vegetation:
Blue oak and annual grasses
Component Properties and Qualities
Slope:
15 to 30 percent
Runoff:
Medium
Surface features:
Polygonal cracking pattern, approximately 24 inches in diameter.
Percent area covered by surface
coarse fragments: None noted.
Depth to restrictive feature:
Bedrock (lithic)—20 to 40 inches
Slowest permeability class:
Slow above the bedrock
Salinity:
Not saline
Sodicity:
Not sodic
Available water capacity:
About 4.5 inches (Low)
Component Hydrologic Properties
Present flooding:
None
Present ponding:
None
Current water table:
None noted.
Natural drainage class:
Well drained
Interpretive Groups
Land capability irrigated:
Not calculated
Land capability nonirrigated: 4e-5
Typical Profile
A—0 to 5 inches; silty clay
Bw—5 to 9 inches; silty clay
Bss1—9 to 19 inches; silty
clay
Bss2—19 to 26 inches;
gravelly silty clay
BC—26 to 35 inches; extremely
gravelly silty clay
R—35 inches; unweathered
bedrock
Estimated Minor Components
Contra Costa loam and similar soils
Composition:
0 to 7 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Sideslopes on hill
Ayar clay and similar soils
Composition:
0 to 4 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Sideslopes on hill
Capay clay and similar soils
Composition:
0 to 3 percent
Slope:
0 to 5 percent
Component geomorphic setting:
Basin floor
Balcom silt loam and similar soils
Composition:
0 to 2 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Sideslopes on hill
Millsholm loam and similar soils
Composition:
0 to 2 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Sideslopes of hill
Rock outcrop
Composition:
0 to 1 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Mountain, hill
Unnamed
Composition:
0 to 1 percent
Slope:
15 to 30 percent
Component geomorphic setting:
Channel
Additional Component Properties
See "Chemical Properties of Soils" table and the "Physical Properties of Soils" table for component horizon data.
For additional component horizon data, see the "Soil Properties" section of this publication.
A typical soil description with range in characteristics is included, in alphabetical order in the "Classification of the Soils" section.
Use and Management
Major uses:
Livestock grazing
For information about management, see the "Use and Management" section
of this publication.