Before you venture on a self-guided tour through the Sibley Volcanic Regional Preserve east of San Francisco Bay, get started with the history and geologic past of this unique place by browsing the interpretive panels and displays on the patio of the unstaffed visitor center at the park entrance. There, the rock display, entitled “Sibley's Geological Treasures,” shows a collection of rocks related to various events that happened during the 10-miilion-year history or volcanic eruption and mountain uplifting along earthquake faults of the Bay Area:
- Autoclastic basaltic breccia
- Basaltic breccia from top of a flow
- Basaltic breccia with limestone matrix
- Conglomerate from Orinda Formation
- Cretaceous sandstone
- Lapilli agglomerate
- Massive basalt lava
- Rhyolite tuff
- Ripple-marked pebbly sandstone
- Vesicular basalt lava
The Sibley Preserve is a great place for nature studies as well as hiking and mountain biking. It includes the Pond Trail, Quarry Trail and Volacanic Trail. and the Bay Area Ridge Trail/Skyline Trail is going through the preserve. Along particular trail segments you may want to view and explore the many geologic features reminding you that you are on top and between ancient remains of an extinct volcano; yet an active fault system.
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