Where You are Standing
The Pedro Point Headlands are a mix of sedimentary rocks originally deposited as sand, mud and gravel off the coast of Southern CA, forming just after the dinosaurs ceased to exist about 65 million years ago. The thick sediments accumulated and formed into rock. When the San Andreas Fault started to develop about 28-40 million years ago, the rocks started moving Northward along with pieces of Sierra Nevada granitics (containing granite). Tectonic plate movements folded the sedimentary rocks almost vertically in places. An impressive example of this layered vertical uplift geology can be viewed at Pedro Pt. summit, looking west to the San Pedro rocks at the surf line.
The Farallon Islands to the west were the shoreline during the last ice age 11,000 years ago when San Pedro creek flowed another 25 miles to meet the sea.
Rocks in this area are Paleocene (about 60 million years ago), sedimentary rocks, Cretaceous (about 90 million years ago), and granitic rocks of the Salinian block, which is a section of crust that formed here by the San Gregorio fault to the Northeast.
Pacific Ocean shoreline rise during the last 17,000 years. Graphic Courtesy Ken LaJoie modified by Stephen Johnson
The San Andreas Fault forms the eastern margin for most of the block, which extends into Southern California. The quartz-rich granitics are very similar to those of the Sierra Nevada, formed by plutonic processes - forming several kilometers below the land surface in what was then an arc of active volcanoes in Southern California. Overlying the deep plutonic granitics that represent the basement foundation, are volcanic, sedimentary and metamorphic rocks, many of which have been eroded as they have been uplifted and exposed to earth surface processes of weathering and water flow. The Pedro Point Headlands are built on this foundation with Paleocene rocks at the surface.