Science Buzz Cafe # 436 Point Reyes National Seashore:The Geology & Scenery with Geology Dude

Point Reyes National Seashore:The Geology & Scenery – Richard Ely, Geology Dude
Geology Dude will describe the geologic history of the park and show numerous photos, with particular attention to the sea cliffs where the best exposures are. He will also show photos of correlative rocks at Point Lobos, the Santa Cruz coast, Bodega head and Salt Point, as well as typical Franciscan rocks of Marin County.

Point Reyes has famously been called an “island in time” because it has escaped the development that has ruined so much of the California coastline. This is true in geologic sense as well, because the park lies on the western side of the San Andreas fault and the rocks exposed there are vastly different from the Franciscan rocks that underlie the rest of Marin County.

The oldest rocks of the park, the granitic plutons of the headlands and Tomales Point originated near the present Mojave Desert in Southern California and have been moved north along the San Andreas fault in the last six million years. The conglomerates of the headlands, visible on the lighthouse trail, are closely related to the conglomerates of Point Lobos. These areas have been separated by movement on the San Gregorio fault, another great strike-slip fault of the San Andreas system.

The sedimentary rocks that underlie the southern part of the park were once opposite Santa Cruz County, where identical rocks are exposed on the east side of the San Gregorio fault.