page_title: Carrizo Plain
section_title: Soil taxonomy
hierarchical_section_title: Carrizo Plain / Geology / Soil taxonomy
caption_attribution_description: Soda Lake in Carrizo Plain National Monument, central California.
context_page_description: The Carrizo Plain across, in southeastern San Luis Obispo County, California, about 100 miles (160 km) northwest of Los Angeles. It contains the 246,812-acre (99,881 ha) Carrizo Plain National Monument, and it is the largest single native grassland remaining in California. It includes Painted Rock in the Carrizo Plain Rock Art Discontiguous District, which is listed on the National Register of Historic Places. In 2012 it was further designated a National Historic Landmark due to its archeological value. The San Andreas Fault occurs along the eastern edge of the Carrizo Plain at the western base of the Temblor Range.
context_section_description: The parent materials for soils in the Carrizo Plain are predominantly alluvium deposits.  Alluvium is soil that has been deposited by rivers or flowing water.  The Paso Robles formation is a Pleistocene aged alluvium deposit that reaches up to 3,000 ft (900 m) thick near the San Andreas fault and thins out towards the north and west.  The Paso Robles formation is a well known aquifer that has been reliably productive for ground wells throughout the area.  The upper layers of soil are more recent alluvium.  This recent layer is thickest near Soda Lake and thins out towards the mountains to the east and west.  Throughout the valley the soil composition varies greatly and includes clay loams, silty clay loams, loams, sandy loams, and gravelly loams.   The sandier soils tend to reside near the slopes of the valley and provide greater drainage while the soils with more clay are located on the valley floor near Soda Lake, and have much poorer drainage.   The soils in the Carrizo Plain have very low fertility because of their high alkalinity content and low rainfall due to the semi-arid climate.
caption: Soda Lake, view to southeast
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