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Mount Diablo Geology

Wind cave
Photograph by Roi Peers

Erosion "wind caves" are common features in the "Domengine" sandstone near Rock City.

Geology: Our understanding of the geological history of the rocks and structure of Mt. Diablo has undergone major changes during the past 30 years, and even now geologists are still trying to unravel the complicated history of the mountain. This complex history is not unique to the mountain, but to our region as a whole, since Mt. Diablo has been caught up in the processes that have shaped the Coast Ranges over the last several million years. Paleontology: Mount Diablo State Park contains geological formations rich in fossil resources. Marine mollusks of Miocene age are abundant along the southern flank of the mountain. Fossil plant material is also common in this area. Along the southern boundary, 9 million year old river deposits have yielded a large number of vertebrate fossil fragments including sabre-tooth cats, mastodons, horses, camels, and llamas.

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"It is clear that geology is not a static field - our interpretations of the landscape are continually changing as we learn more when we look at the landscape with new ideas."
- Doris Sloan, UC Berkeley