By: Phaneritic
Image: “Geological Gems of California State Parks” by California Geological Survey ⧉
Subject: Ryan J Hollister
License: Creative Commons Non Commercial ⧉

Uploaded: 29 Nov 2023
Last Updated: 29 Nov 2023

580 megapixels
44,041 x 13,161 pixels
146.8 in X 43.9 in at 300dpi

The shoreline of Montaña de Oro State Park is an ideal place to examine and explore geologic features such as tilted and folded rock outcrops. These rocks show different strata that were deposited in horizontal layers sequentially through time. About six million years ago, these beds were deposited as flat layers, one on top of another. The layers of rock record past conditions. Tectonic forces over the past three million years have tilted the beds. Where these rocks are exposed along the coast, the sloping surface reflects just the top of a thick stack of sloping strata with the oldest beds at the bottom and the youngest beds at the top. Capping the marine strata are gravels that partly covered a marine terrace. These gravels are much younger than the underlying strata and are relatively undeformed. The contact between these two deposits is called an unconformity, and represents an extended gap of time for which the geologic record is incomplete, either due to no deposition or to erasure by erosion. Differential erosion has preferentially etched away the softer rocks, leaving ridges of harder rock as ledges extending into the surf.