Significant geographic features include the Transverse Ranges and the Peninsular Ranges. Major rivers in the region include the Los Angeles River, San Gabriel, San Diego, San Luis Rey, Santa Ana, Santa Clara, Santa Margarita, and Ventura.
The climate in the region ranges from Mediterranean to subtropical steppe. Annual precipitation in the region ranges from more than 40 in (1,000 mm) in the mountains to less than 10 in (250 mm) in some valleys, with an overall average of 17.6 in (450 mm) for the region.
Alluvial groundwater basins in the South Coast hydrologic region
An alluvial groundwater basin is essentially the top level of an aquifer, above less-permeable rocks below, such as like limestone and shale.[1](Alluvium (from Latinalluvius, from alluere 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings.[2])
^Jackson, Julia A., ed. (1997). "alluvium". Glossary of geology (Fourth ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
^ ab"Bulletin 118 (South Coast, Chapter 6)"(PDF). This article includes material published by the U.S. state of California that is believed to be in the public domain.