Mount Diablo is a mountain of the Diablo Range, in Contra Costa County of the eastern San Francisco Bay Area in Northern California. It is south of Clayton and northeast of Danville. It is an isolated upthrust peak of 3,849 feet, visible from most of the San Francisco Bay Area. Mount Diablo appears from many angles to be a double pyramid and has many subsidiary peaks, the largest and closest of which is the other half of the double pyramid, North Peak, nearly as high in elevation at 3,557 feet, and is about one mile northeast of the main summit.
The mountain is in Mount Diablo State Park, administered by California State Parks.