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primarily on percentage of silt, sand, and organic matter (up to 4 percent) and
on soil structure and permeability. The higher the K value, the more
susceptible the soil is to sheet and rill erosion by water. Numerical erosion
factor K values were listed for soils included in the SCS Soil Survey of
Angeles National Forest Area (USDA, 1991). Erosion factor K values for
soils on land outside the National Forest Land were descriptive and ranged
between low and very high (USDA, 1970).

Drainage class: This property refers to the frequency and duration of periods
of saturation or partial saturation during soil formation, as opposed to altered
drainage, which is commonly the result of artificial drainage or irrigation, but
may also be caused by the sudden deepening of channels or the blocking of
drainage outlets. Seven classes of natural soil drainage are recognized,
ranging from excessively drained to very poorly drained.

Soil Manageability: Soils within the Angeles National Forest were classified
according their soil manageability. Certain features of the land affect the
relative ease of management with mechanized equipment. Soil manageability
classification rates soil and their topography on the basis of features that
reduce the ease of equipment operation and features that increase the need
for soil protection measures. Soil manageability classes are the ratings that
are applied to the individual components of a soil map unit. Soil
manageability classes are represented by the numerals 1 to 4. Class 1 is the
easiest to manage and class 4 is the most difficult. Letter symbols are added
to classes 2, 3, and 4 to identify specific soil problems affecting management.

Limitation Rating for Allowable Soil Pressure: Soils included in the 1970 SCS
Soil Survey were rated for allowable soil pressure. Soils were classified on
their ability to withstand pressure imposed on them by foundations, as defined
in the Unified Building Code, 1967, Ed., Vol. 1, Sec. 2804. Three soil
limitation descriptors are utilized based on the soil’s texture and its
consistence when dry. The three limitation descriptors are slight, moderate,
and severe.

Road Location: Features that adversely affect the location of roads include a
high water table, soil texture, steep slopes, shrink-swell potential, and depth
to bedrock or hardpan. These features were discussed in the 1970 SCS soil
survey for soils located on private land within the site.

Engineering Classification of Soil: One system utilized by the American
Association of State Highway Officials (AASHO) classifies soils into seven
principal groups. The groups range from A-1 (gravelly soil having high
bearing capacity, the best soils for subgrade) to A-7 (Clayey soils have low

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