The Yucaipa Subbasin lies within the Upper Santa Ana River Basin Hydrologic Region (DWR basin number 8-002.07) and underlies an area of approximately 25,300 acres under portions of the cities of Calimesa, Redlands, and Yucaipa, as well as unincorporated San Bernardino and Riverside Counties (Figure 1-1, Vicinity Map of the Yucaipa Subbasin Plan Area). The Yucaipa GSA jurisdictional boundary consists of the entire Yucaipa Subbasin within San Bernardino County and Riverside County.
The Subbasin is bounded to the north and northeast by the San Andreas Fault Zone and the San Bernardino Mountains, to the east by the Yucaipa Hills, to the south by San Timoteo Wash and the San Timoteo Badlands, and to the west by the Crafton Hills and the San Bernardino Basin Area. The Yucaipa Subbasin ranges in elevation from 1,300 feet to approximately 5,100 feet.
DWR designated the Yucaipa Subbasin a high priority basin based primarily on its reliance on groundwater for water supply. However, the Subbasin is not in a state of critical overdraft. Under SGMA, GSAs “have the responsibility for adopting a Plan that defines the basin setting and establishes criteria that will maintain or achieve sustainable groundwater management” (California Water Code, Section 350.4[e]). The requirement of the GSP is to maintain or achieve sustainable groundwater management in the Yucaipa Subbasin by 2042.
The Yucaipa Subbasin is compartmentalized into four management areas. The boundaries of the management areas were based on the geologic structures that influence groundwater flow, the locations of groundwater-dependent ecosystems, and the locations of water supply wells by different water purveyors. The following management areas, listed in order from the highest to lowest along the hydraulic gradient in the Subbasin, are based on the geologic structures that defined the hydrogeologic subareas in the Subbasin, the distribution of public water supply wells, and presence of GDEs:
1. North Bench Management Area
2. Calimesa Management Area
3. Western Heights Management Area
4. San Timoteo Management Area