Clay Soils, Soil Survey Geographic (SSURGO) database for San Diego County, California, USA

The SSURGO soils dataset of San Diego County was used to select only clay soil types (Altamont, Auld, Bosanko, Diablo, Diablo-Olivenhain, Huerhuero, Linne, Olivenhain, Redding, Salina, Stockpen, and Clayey Alluvial Land), which comprise this dataset. 

Original description of the entire dataset:
This data set is a digital soil survey and generally is the most
detailed level of soil geographic data developed by the National
Cooperative Soil Survey. The information was prepared by digitizing
maps, by compiling information onto a planimetric correct base and digitizing, or by revising digitized maps using remotely sensed and other information.

This data set consists of georeferenced digital map data and
computerized attribute data. The map data are in a soil survey area
extent format and include a detailed, field verified inventory of soils and miscellaneous areas that normally occur in a repeatable
pattern on the landscape and that can be cartographically shown at the scale mapped. A special soil features layer (point and line features) is optional. This layer displays the location of features too small to delineate at the mapping scale, but they are large enough and contrasting enough to significantly influence use and management. The soil map units are linked to attributes in the National Soil Information System relational database, which gives the proportionate extent of the component soils and their properties.

1:20,000