Backcountry Geology Guide

Thanks to Merton Hill & Annilia Paganini Hill for this Geology Information

Geologic processes, including floods, wind and water erosion, volcanic eruptions, landslides, and earthquakes, continuously shape this land. Records of these events await your discovery in the rocks of Crystal Cove State Park.

Beginning 25 million years ago, sediments (sand, silt, clay, and skeletons) slowly accumulated in shallow Pacific Ocean waters and formed the geologic layer known today as the Vaqueros Formation, the oldest exposed rock unit in the park.

Over the next several million years, the Crystal Cove area sank deeper into the ocean. Sediments deposited during this time formed the Topanga Formation in an oceanic environment deeper than the Vaqueros. Composed of units slightly varying in rock characteristics, the Topanga Formation is subdivided into three separate “members”. The oldest and lowest member is the Bommer, overlain by the Los Trancos and Paularino Members.

Between 15 and 12 million years ago, sediments forming the San Onofre Breccia were deposited from islands offshoreasCaliforniawastornapart by tectonic forces. Magma (molten rock) worked its way up through joints and faults, forming andesite and diabase dikes (igneous intrusions cutting across the rock fabric) and flows.

Explore 25 million years of the earth’s history at Crystal Cove State Park. Discover the secrets of the rocks shaped by the sea, sand, magma, and ancient life.

Hike through the backcountry and enjoy the ever-changing landscape.

In the Geology Guide below, to go from page to page, pass your mouse over  the bottom of each page and select the next arrow.

Follow this detailed guide to learn the geology of the Backcountry. Download here.