Geology of Agua Dulce

General Facts

Agua Dulce rests in the Sierra Pelona Valley which is composed of an early Quaternary valley floor. It is one of the last remnants of a floor which covered much of this region. The floor here is currently being eroded by the tributaries of the Santa Clara River. Signs of this are easy to find. Many houses along Agua Dulce Canyon Road are built on top of terraces. These terraces once were at stream level. This type of erosion is called Headward Erosion. The rock underlying this valley floor is mostly Oligocene in age and is a part of the Vasquez Formation. The Sierra Pelona Mountains to the north are made of Precambrian Pelona Schist. These mountains are a part of the Transverse Ranges as they generally run west to east. Vasquez Rocks, to be explained in better detail later, are composed of steeply tilted Oligocene Vasquez Formation fanglomerates and the shape is due to erosion of the softer parts of the formation. In nearby Tick Canyon, a borax mine flourished from 1906 to about 1920. The remains can still be seen along Davenport Road about half way between Sierra Highway and Agua Dulce Canyon Road. Many minerals can be found there including howlite, colemanite, ulexite, and many others. A great website has been produced covering the mineralogy of the locality in much greater detail by the Mineralogical Society of Southern California.

Micro-fault within layers of sandstone in the Tick Canyon Formation.

Rivers and Drainage

All the streams in this area drain southerly into the Santa Clara River via Agua Dulce Canyon. These streams are eroding headward into the Sierra Pelona Valley floor creating a terraced appearance.

Faults and Folds

The Elkhorn Fault, one of the faults in the area, runs in a generally east-west line near Escondido Canyon Road. The signs of folding are shown in road cuts and at Vasquez Rocks. They are steeply dipping away from the axis of a large anticline.

Photo of Vasquez Rocks

Another view of the Agua Dulce area from above State 14.

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