The Whitewater River is the principal drainage for the southeastern portion of the San Bernardino Mountains. It debouches into San Gorgonio Pass where it has constructed a large, side entry alluvial fan. Strong west winds blow down the pass across the fan, pick up sand and dust, and carry them down the trough into North Palm Springs, sand blasting automobiles making their way up the pass on I-10.
Take exit 114 off I-10 near Cabezon to explore Whitewater Canyon. At the mouth of the canyon an outlet sells decorative building stone obtained from two quarries upstream. The stone is gneiss and schist used for building facings, patios, walls, fireplaces, and other masonry work. Colorful decorative gravel, locally called Palm Springs Gold and obtained from another quarry, is a beautiful mix of white quartz, violet mica schist, pink piemontite, and various hydrothermally altered orange and reddish-brown rocks. These minerals and rocks are derived from metamorphic rocks farther upstream in the heart of the San Bernardino Mountains.
From the mouth of the wash proceed north and upstream along a two-lane road about 1 mile through sparse desert vegetation, until you abruptly encounter an oasis of lush vegetation in the bottom of the wash. The oasis marks the trace of the Coachella Valley–Banning fault, which strikes nearly east across the canyon, placing Cabazon fanglomerate of late Pleistocene age on the downstream side of the fault against gneiss and granite of Proterozoic age on the upstream side. The oasis is located where subsurface water percolating southward through canyon alluvium is dammed by impervious clay fault gouge along the fault. The water table is thus higher on the upstream side of the fault, so that springs flow at the surface and water the oasis.
The Whitewater fault lies within the east canyon wall, almost parallel to the canyon, and juxtaposes old alluvium against Coachella fanglomerate of late Miocene age. You can view a splendid exposure of the fanglomerate at the terminus of the road adjacent to a trout farm about 5 miles from the mouth of the canyon.
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Roadside Geology of Southern California 