Transverse Ranges - Geology

Geology

The Transverse Ranges represent a complex of tectonic forces and faulting stemming from the interaction of the Pacific Plate and the North American Plate along the San Andreas Fault system. Their orientation along an east-west axis as opposed to the general southeast-northwest trend of most California ranges results from a pronounced step in the San Andreas Fault, the cause of which is a subject of intensive ongoing study. The San Andreas Fault is a dextral strike-slip fault with a right step, causing the mountains. Their elevation is somewhat better understood as a consequence of this step. The crust atop the Pacific Plate south of the ranges does not easily make the turn westward as the entire plate moves northwestward, forcing pieces of the crust to compress and lift.

The crust which comprises the Transverse Ranges is part of what is known as the Salinian Block, originally a piece of the North American Plate which was broken off what is now northwestern Mexico as the Gulf of California rifted open.

Physiographically, the Tranverse Ranges are a distinct physiographic section of the larger Pacific Border province, which in turn is part of the larger Pacific Mountain System. They exhibit extreme differences in geologic age and composition, varying from sedimentary rocks in the western Santa Ynez and Santa Monica mountains to primarily granitic and metamorphic rock in the eastern regions, where they terminate abruptly in the San Gabriel and San Bernardino mountains.