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Trail Through Time

A Journey Through 180 Million Years of Geologic Time
Parking access at Rock City, Sunset Picnic Area, Juniper Campground and Lower Summit Parking Lot


With 20 trailside interpretive panels, the complete Trail is 6.25 miles in length with a vertical elevation gain of 2,940 feet. It can also be traversed in reverse down the mountain walking over older to younger rocks. Because the panels are independent of each other, shorter segments of the Trail can also provide an informative geology experience.

A Geologic Story Book

Like chapters in a book, the rocks of Mount Diablo tell a story of previous landscapes, climates, and life forms as well as epic journeys of tectonic plates. Trail Through Time panels are placed along the trail to help you read the geologic story written in the rocks as you travel through 180 million years of geologic time. Interspersed with the geologic panels are panels on history, geography, and ecology.

The Journey Begins

Your journey back in time begins near the southern park boundary on Sycamore Creek. As you walk north toward the mountain, you will first journey over 12 million-year-old rocks formed in a shallow sea. Look for shell fossils as you walk. At Rock City, you will pass over 50 million year-old sandstone with unusual erosion features, such as the Wind Caves and Sentinel Rock. You will then cross a rock bed exposing numerous marine snail fossils.

When Reptiles Ruled

Continue your journey as you cross over the boundary between the “Age of Mammals” into the “Age of Reptiles.” In a short distance you will cross a major fault along which the core rocks of the mountain have been pushed up and over younger rocks. As you continue to climb toward the summit, you pass the former site of a hotel built in the late 1800’s.

Walking over Older Rocks

As you walk among the varied and oldest rocks of the mountain’s core, you will find contorted red beds of chert made from the skeletons of tiny marine animals, followed closely by an exposure of graywacke sandstone. A short distance ahead is an outcrop of greenstone, an altered submarine volcanic rock. The chert, graywacke, and greenstone rocks have undergone massive compressive forces.

The Journey Ends

At the end of the Trail Through Time is an overlook to the north with a view over displaced igneous rocks that were originally formed as ocean crust at a distant spreading center. The spectacular view from the summit makes your climb all worthwhile.

The DEDICATION CEREMONY for the Trail Through Time was held in the Fall of 2008. Work will continue to upgrade the trail alignment and develop outreach programs to encourage public use. We invite suggestions from trail users to help us improve the value of the trail as an educational and hiking experience.

California State Parks does not discriminate against individuals with disabilities. Prior to arrival, visitors with disabilities who need assistance should contact the park at the phone number below. To receive information in an alternate format, write to the following address:

Mount Diablo State Park 
96 Mitchell Canyon Road 
Clayton, CA 94517 
(925) 837-6119 
TTY relay service, 711

Brochure compiled by Mount Diablo Interpretive Association in conjunction with California State Parks, University of California Museum of Paleontology, and the National Natural Landmark Program of the National Park Service. In recognition of the mountain’s importance to our natural landscape, a state park was established in 1931. It was designated a National Natural Landmark by the National Park Service in 1982.

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