3.9 GEOLOGY, SOILS, SEISMICITY EXECUTIVE SUMMARY This section describes the types of soils present within the City’s Planning Area. Development constraints associated with soil hazards, subsidence, and geologic hazards are discussed along with City development standards. The City’s Planning Area consists of its incorporated boundaries and adopted Sphere of Influence (SOI). The County’s Planning Area consists of unincorporated land within the One Valley One Vision (OVOV) Planning Area boundaries that is outside the City’s boundaries and adopted SOI. Together, the County and City Planning Areas comprise the OVOV Planning Area. With implementation of the proposed General Plan goals, objectives, and policies and mitigation measures defined in this section, potential impacts from geology, soils, and seismicity would be less than significant. EXISTING CONDITIONS Soils Various soil types exist within the City’s Planning Area as shown on Figure 3.9-1, Soil Types within the City’s Planning Area. Saugus loam, 30 to 50 percent slopes, eroded (ScF2) is the most abundant type of soil within the City’s Planning Area with approximately 7,689 acres. A detailed description of each soil type found within the City’s Planning Area is presented in Appendix 3.9 of this environmental impact report (EIR) and corresponds with the soil types mapped on Figure 3.9-1. Each soil characteristic is identified to determine the Capability Classification of the soil on site, which in turn determines the predicted productivity of the soil if it were under agricultural production; the majority of the soils within the City’s Planning Area would be used for wildland/grazing areas, and would not be able to economically or physically sustain agricultural production. The following text describes the soil associations found within the City’s Planning Area. A soil association is a landscape that has a distinctive proportional pattern of soils. It normally consists of one or more major soils and at least one minor soil, and is named for the major soils. The soils in one association may occur in another association but in a different pattern. A soil series is the lowest category of the national soil classification system. The name of a soil series is the common reference term, used to name soil map units. The soil series are presented in this section by their location (i.e., Upland, Alluvial Fans, Alluvial Fans and Floodplains, Terraces, and Terraces and Foothills). Appendix 3.9 provides a cross-reference to the soil type and soil association. Impact Sciences, Inc. 3.9-1 One Valley One Vision Draft Program EIR 0112.023 City of Santa Clarita September 2010 3.9 Geology, Soils, Seismicity Saugus-Castaic-Balcom Association This association is located on foothills and mountains on gently sloping to very steep, well-drained soils that are loam to silty clay loam throughout; deep to moderately deep over soft sandstone or shale. Some area of this soil association is adjacent to Ventura County, and others are north and south of the Santa Clara River and its tributaries near Saugus. Saugus soils make up about 50 percent of this association. Castaic soils make up about 25 percent of this soil association and Balcom soils about 20 percent. Mocho, Sorrento, and other alluvial fans make up the remaining 5 percent of this soil association. Saugus Series (Uplands) Soils of the Saugus series are well drained and are located on uplands. These soils formed on weakly consolidated sediment that contained pebbles and cobblestones in some places. Slopes range from 15 to 50 percent. Elevations range from 1,300 to 2,250 feet. Vegetation consists of dense stands of chamise and candlestick yucca with an understory of annual grasses, forbs, and remnant stands of perennial grasses. Average annual precipitation ranges from 14 to 16 inches, average annual temperature is about 63 degrees Fahrenheit, and the frost-free season ranges from about 275 to 300 days. In a typical profile, the surface layer is grayish-brown loam about 15 inches thick. Below is grayish-brown loam about 15 inches thick. Below is grayish-brown loam underlain by weakly consolidated sediment at a depth of 42 inches. These soils are used for range and for homesites. They also are used for wildlife and watershed purposes.1 Castaic Series (Uplands) The Castaic series consists of well-drained soils that formed in material from soft shale and sandstone. These soils are located on uplands with slopes from 2 to 65 percent. Elevations range from 1,250 to 1,500 feet. Vegetation consists mainly of annual grasses and forbs, but stipa, a perennial grass, grows in small areas and brush grows in some places on north slopes. Average annual precipitation ranges from 14 to 16 inches, average annual temperature is 63 degrees Fahrenheit, and the frost-free season ranges from 275 to 300 days. In a typical profile the surface layer is pale-brown silty clay loam underlain by soft shale and sandstone at a depth of about 26 inches. These soils are used for dryland small grains and pasture, for range, for watershed, and as wildlife habitat.2 1 United States Department of Agriculture, “Soil Survey Antelope Valley Area California,” Soil Conservation Service in cooperation with University of California Agricultural Experiment Station, 1970. 2 United States Department of Agriculture, “Soil Survey Antelope Valley Area California,” 1970. 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