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A Tour of the Western Transverse Ranges
Photos and notes by your About Geology Guide
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The Transverse Ranges make up a major physiographic region of California, an east-west wall of mountains running from Points Concepcion and Arguello, near Lompoc, through the Joshua Tree region. The western and eastern halves are geologically distinct, but they arise from the same plate-tectonic situation: northward translation along the North American plate boundary (the San Andreas fault zone) meets westward extension of the Basin and Range province. Between these conflicting forces the rocks of the region warp, stretch and rotate into a rugged textbook of physical geology.

State route 33 runs the length of the San Joaquin Valley, a country cousin of mighty route 99 that connects some of the loneliest towns of the valley. Where 99 surges through Bakersfield, 33 winds through tiny Taft and into the western foothills of the California oil district, then continues southward into the Transverse Ranges at the top center of the geologic map below.

Western Transverse Ranges geology. Santa Barbara at bottom left; I-5 meets the Grapevine grade at upper right corner, the end of the San Joaquin Valley. San Andreas fault zone cuts across upper right. Cuyama pull-apart basin (top left) is filled with young sediment; route 33 runs down its east side and into progressively older rocks marked by cooler colors: Quaternary/Pliocene (QPc), Miocene (M) and Eocene (E). Some areas of Oligocene (Oc) rocks are mapped separately further south. Mesozoic granites in red are carried here from the east; Franciscan rocks in olive and purple make their southernmost appearance. Map derived from California State Geologic Map, 1977. Follow along on this enlarged version (opens a separate window).

These photos were taken on a late winter day in 2002. It can be snowy or blasting hot at different times of year, and services are very sparse. Be prepared if you go here.

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