Hydrologic Region Colorado River
Coachella Valley Groundwater Basin
Last update 2/27/04
Coachella Valley Groundwater Basin,
San Gorgonio Pass Subbasin
• Groundwater Basin Number: 7-21.04
• County: Riverside
• Surface Area: 38,650 acres (60 square miles)
Basin Boundaries and Hydrology
The portion of the Coachella Valley Groundwater Basin that lies entirely
within the San Gorgonio Pass is described as the San Gorgonio Pass
Subbasin (DWR 1964). This subbasin is bounded on the north by the San
Bernardino Mountains and by semi-permeable rocks, and on the south by the
San Jacinto Mountains. A surface drainage divide between the Colorado
River and South Coastal Hydrologic Study Areas bounds the subbasin on the
west. The eastern boundary is formed by a bedrock constriction that creates
a groundwater cascade into the Indio Subbasin (DWR 1964).
Average annual rainfall over the subbasin ranges from 15 to 18 inches. The
San Gorgonio River flows intermittently over the subbasin and is the main
surface drainage feature for the subbasin (Bloyd 1971). Precipitation in the
northern San Bernardino Mountains contributes its runoff to the San
Water Bearing Formations
The main water bearing deposits in the subbasin are Holocene and
Pleistocene age alluvium and Pliocene to Pleistocene age San Timoteo
Alluvium. Holocene alluvium is mostly gravel and sand and, where
saturated, would yield water readily to wells. Within the subbasin, these
deposits lie largely above the water table and contribute little water to wells.
Holocene alluvium is found in the tributaries of the subbasin and allows
runoff to infiltrate and recharge the subbasin (DWR 1987).
Older, Pleistocene age alluvium contains sand and gravel, but also large
amounts of clay and silt. These deposits yield moderate amounts of water to
wells (DWR 1987).
San Timoteo Formation. The Pliocene to Pleistocene age San Timoteo