Page 24 - Beaumont Basin Watermaster

Section 3
Water Quality Conditions

Currently, the Basin is in a dry period that began in 2011. During the last 10 years, two of the
five years with the lowest precipitation ever recorded at Station 13 have occurred; 7.4 inches
(lowest ever) in 2013 and 8.07 inches in 2009. It should be noted that the average
precipitation during the base period (1997-2001) used to determine the Safe Yield of the Basin
was 13.43 inches, close to 25 percent below the 100-year long-term average for the Basin and
approximately 12 percent below the 25-year precipitation average.

3.1.2 Surface Water Hydrology

There are three significant drainage systems that overlie the Beaumont Basin: the San
Timoteo Creek drainage system which is tributary to the Santa Ana River; the Potrero Creek
drainage system in the San Jacinto watershed; and the Smith Creek drainage system tributary
to the White Water River which is part of the Salton Sea drainage basin.

Surface water flows originate in the San Bernardino Mountains to the north of the Basin. The
streams and creeks that flow into the Beaumont Basin are dry for most of the year with
occasional runoff during rainfall events. There are no stream gages in the Basin that can be
used to estimate surface water recharge to the Basin or discharge from the Basin. Afghanistan

3.1.3 Hydrogeology

3.1.3.1 Regional Geologic Context
The Beaumont Basin is located in the San Gorgonio Pass, a low-relief highland that is
bordered on the north by the San Bernardino Mountains, on the southeast by the San Jacinto
Mountains, and on the west by the San Timoteo Badlands. Surface sediments in the
Beaumont Basin and nearby lowlands consist of unconsolidated to semiconsolidated
Quaternary alluvium. Surrounding the alluvial sediments are semiconsolidated rocks of the
San Timoteo Formation and igneous and metamorphic rocks that make up the San Jacinto
and San Bernardino Mountains (see Figure 3-2). The San Timoteo Formation is composed
primarily of sandstone, conglomerate, siltstone, and mudstone (Rewis, et al., 2007). The
igneous and metamorphic rocks form the crystalline basement rocks in the area (Bloyd, 1971).
The unconsolidated Quaternary alluvium and the upper portion of the underlying San Timoteo
Formation constitute the water-bearing aquifer of the Beaumont Basin (Rewis, et al., 2007).

3.1.3.2 Faults
The boundaries of the Beaumont Basin are based on faults that often form barriers to
groundwater flow (Bloyd, 1971). Major faults in the area include the Banning and Cherry
Valley faults, which form the northern boundary of the basin (see Figure 3-2). Groundwater
levels within the Beaumont Basin are generally lower than groundwater levels in the
surrounding areas. Along the Banning Fault, groundwater levels on the north side of the fault
and outside the basin are as much as 400 ft higher than groundwater levels on the south side
of the fault and inside the basin. The same condition has been observed along the southern
Beaumont Basin boundary.

Beaumont Basin Watermaster 2018 Annual Report – DRAFT - February 2019 3-2