Geology and Hydrogeology of the Yucaipa Groundwater Subbasin, San Bernardino and Riverside Counties, California

Scientific Investigations Report 2021-5129
Prepared in cooperation with San Bernardino Municipal Valley Water District
By:  and 



The Yucaipa groundwater subbasin (referred to in this report as the Yucaipa subbasin) is located about 75 miles (mi) east of of Los Angeles and about 12 mi southeast of the City of San Bernardino. In the Yucaipa subbasin, as in much of southern California, limited annual rainfall and large water demands can strain existing water supplies; therefore, understanding local surface water and groundwater conditions is essential for managing these resources. To better understand the hydrogeology and water resources in the Yucaipa subbasin, especially groundwater, the San Bernardino Valley Municipal Water District and the U.S. Geological Survey initiated a cooperative study to evaluate the hydrogeologic system of the Yucaipa subbasin and the encompassing Yucaipa Valley watershed. Previous studies of the area provided information on general geologic and hydrologic conditions, but this study provides the first comprehensive definition of the hydrogeology of the subsurface throughout the entire subbasin.

The Yucaipa subbasin is located between the northwest trending San Andreas fault zone and San Jacinto fault. Several northeast-trending dip-slip faults dissect the Yucaipa subbasin, providing the mechanism for structural relief within the sediment-filled subbasin and between the subbasin and surrounding mountains and highlands. Several of these dip-slip faults have been previously identified as potential barriers to groundwater flow. This report provides a synthesis of previous studies and a discussion of the geologic interpretations that were used as the foundation for hydrogeologic classification of the Yucaipa subbasin. Notably, this report (1) adopts the recently named and classified sedimentary deposits of Live Oak Canyon geologic formation and extends the mapped distribution of the formation into the Yucaipa subbasin, and (2) adopts the interpretation that activity along the Banning fault predates the deposition of most basin-fill sedimentary materials in the Yucaipa subbasin.

Four hydrogeologic units were classified in the Yucaipa subbasin: (1) crystalline basement, (2) consolidated sedimentary materials, (3) unconsolidated sediment, and (4) surficial materials. The crystalline basement unit forms the bottom boundary of the aquifer system, and the three other units comprise the basin-fill aquifer system. The four hydrogeologic units vary in extent, thickness, and structural relief across the subbasin, with the unconsolidated sediment unit serving as the primary aquifer unit. A three-dimensional hydrogeologic framework model was developed for the Yucaipa subbasin and surrounding area to characterize the thickness, extent, and hydrogeologic variability of the aquifer system. Geologic maps, borehole geophysical logs, drillers’ lithology logs, and depth-to-basement gravity data were used to map and interpolate the subsurface extent and structure of the hydrogeologic units within the subbasin. Faults and structures of geologic and (or) hydrogeologic importance were included in the model for future evaluation of their potential effects on groundwater flow. The resulting hydrogeologic framework is consistent with existing geologic concepts and the tectonic and structural history of the Yucaipa subbasin and surrounding area. The framework is also suitable for use in basin-scale hydrogeologic investigations.

Suggested Citation

Cromwell, G., and Matti, J.C., 2022, Geology and hydrogeology of the Yucaipa groundwater subbasin, San Bernardino and Riverside Counties, California: U.S. Geological Survey Scientific Investigations Report 2021–5129, 58 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments   
  • Abstract   
  • Introduction   
  • Description of Study Area   
  • Geology of the Yucaipa Groundwater Subbasin   
  • Hydrogeologic Framework Model   
  • Summary   
  • References Cited 
Publication type Report
Publication Subtype USGS Numbered Series
Title Geology and hydrogeology of the Yucaipa groundwater subbasin, San Bernardino and Riverside Counties, California
Series title Scientific Investigations Report
Series number 2021-5129
DOI 10.3133/sir20215129
Year Published 2022
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center, Geology, Minerals, Energy, and Geophysics Science Center
Description Report: ix, 58 p.; Data Release
Country United States
State California
County San Bernardino County, Riverside County
Other Geospatial Yucaipa Groundwater Subbasin
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details