Posted 21 April 2016 by A.G. Sylvester ©
CA 1 proceeds west and then north through Lompoc on the Santa Ynez River flood plain. CA 1 crosses the Santa Ynez River about two miles north of the center of town, then climbs upon the broad, chaparral-covered Burton Mesa and heads west to the main gate of Vandenberg Air Force Base. The mesa consists of the Orcutt Sand, a deposit of tan to rusty brown, friable to locally indurated wind-blown sand interbedded with gravel covering a large area between Lompoc and Santa Maria. Gullies notch the plain and expose outcrops of diatomaceous mudstone of the Pliocene Sisquoc Formation and of siliceous shale and porcelanite of the Monterey Shale.
Northward from the Vandenberg AFB gate (PM 28.6), the highway passes across 4 miles of locally deformed Orcutt Sand, being tilted as much as 12 degrees on the flanks of anticlines. The maximum outcrop thickness of the Orcutt Sand is between 50 and 100 feet throughout the Santa Maria area. It is eroded into badlands at the intersection with Firefighter Road (RM 29.9). CA 1 descends the long Harris Grade into San Antonio Valley and Barka Slough (PM 37.1) to Pliocene Sisquoc Formation at the base of the grade.
The low rolling hills on both sides of the highway between Barka Slough and Guadalupe are parts of an extensive series of stacked longitudinal sand dunes of Late Pleistocene to Recent age. Prevailing northwest winds carried the sand inland from coastal beaches.
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Roadside Geology of Southern California 