Much of the rock that makes up Mount Diablo is sedimentary in origin. It was laid down millions of years ago on the floor of the ocean. Within the last one to two million years, a piece of hard, red 160-million-year-old Franciscan rock was pushed up through six to eight miles of overlying rock and soil, tilting and distorting the rock layers and in some places turning them completely upside down. As a result, the fossilized remains of many sea creatures, as well as those of mastodons, saber-toothed cats and three-toe horses have been discovered here

___ Mount Diablo State Park brochure

Natural History of Mount Diablo State Park

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