This polygon shapefile contains information about expansive soil areas in San Joaquin County, California. Expansive soils are those that are prone to large volume changes (swelling and shrinking) and are directly related to changes in water content. Soils with a high content of expansive minerals can form deep cracks in drier seasons or years - such soils are called vertisols. Soils with smectite clay minerals, including montmorillonite and bentonite, have the most dramatic shrink-swell capacity. Soil surveys are conducted by the Natural Resources Conservation Service. This layer is part of a collection of GIS data for San Joaquin County in California.This dataset is intended for researchers, students, and policy makers for reference and mapping purposes, and may be used for basic applications such as viewing, querying, and map output production, or to provide a basemap to support graphical overlays and analysis with other spatial data.