Page 23 - Beaumont Basin Watermaster - 2015 Annual Report

Section 3
Status of the Basin and Administration of the Judgment

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.

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.

3.1.3.3 Groundwater Occurrence and Flow

Groundwater in the Beaumont Basin occurs at depth in the Quaternary alluvium and the
underlying San Timoteo Formation. Groundwater flow within the Beaumont Basin generally
depends on location with respect to a groundwater flow divide which occurs in the center of
the basin, approximately coincident with the Noble Creek drainage (see Figure 3-2). West of
the Noble Creek drainage, groundwater generally flows to the northwest and ultimately as

Beaumont Basin Watermaster 2015 Annual Report – Final – December 2016 3-2