Mount Diablo, California

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Location and topographic map of Mount Diablo and vicinity. Contour interval 100 meters.

Simplified geologic map of Mount Diablo area. Tertiary rocks are buff, Quaternary deposits are light yellow. Cretaceous rocks are green. Principal roads are dark gray; note that alignment of roads and geology is somewhat approximate. Blue arrows show dip and facing directions of homoclinal rocks. Faults are in red.

Interstate 680 runs north-south along the San Ramon valley, which is also the trace of the Calaveras Fault. West of the fault the rocks are folded by transpressional right-lateral shear to form the Berkeley hills. Units that form the cores of synclines are in yellow, those in the cores of anticlines in light brown.

East of the Calaveras Fault is a large anticlinorium, pierced by the rocks of Mount Diablo. The pircement structure is made up of Jurassic Franciscan and Coast Range Ophiolite rocks. JKk is the Knoxville Formation, Jpb is pillow basalt, Jdb is diabase, sp is serpentine, fm is Franciscan melange, fbc is Franciscan basalt and chert, fss is Franciscan sandstone and shale. The peaks are underlain by the resistant basalt-chert complex.

Mount Diablo's isolation and distinctive sugar-loaf, double peak profile makes it one of the most distinctive landmarks in California. This view is from the southwest in Dublin.
View from the east. The north peak, though lower, is nearer in this photo and looks equal in height to the main peak.
Aerial view from the west, approaching San Francisco airport. The two peaks rise above the clouds just left of center. San Francisco Bay is in the middle distance and the San Andreas Fault runs along the hills from center right to lower left.
View from the west near Walnut Creek.
View from the southwest in Dublin. The base of the foreground hills is the north-south Calaveras Fault.
View from the north. The main summit is the peak on the right.
The southern foothills of Mount Diablo. What used to be bucolic ranch land is being rapidly californicated by gated subdivisions. Fortunately there are large tracts set aside for parkland, but everything else is being rapidly paved over.
View from the northeast, with the main summit on the left and behind the nearer north peak.
Aerial view from the southeast. The East Bay cities are in the foreground and the base of the hills is the Hayward Fault. The far edge of the hills, forming a straight line sloping slightly right across the center of the picture, is the Calaveras Fault.
At least a few times a year, Mount Diablo gets snow. Here the snow-covered peak is on the horizon at center. In the forground is San Francisco Bay with salt evaporation lagoons.
Aerial view from the northwest. The Central Valley is the flat expanse in the left distance.
Aerial view of the summit from the northwest.
View of the summit, showing parking area and summit road.
A small mercury mine once operated on the northeast flank of Mount Diablo. I hope that catchment pond is working.

Summit Views

Looking north from the summit with the north peak to the right. At dead center on the horizon is Mount Lassen and the snow-covered northern Sierras are a thin white line on the right horizon. The Sacramento Delta is the water in the middle distance.

It is apparently a myth, alas, that you can see Mount Shasta from here because intervening hills block the view. When atmospheric conditions are right a refracted image can sometimes be spotted.

View northeast.
View to the east. Sierra Nevada on the horizon with the Central Valley between. Most of the hills of the Diablo Range are hogbacks defined by resistant Tertiary and Cretaceous formations.
View southeast. Mount Whitney is not visible from here because of intervening peaks. About half of California is visible from Mount Diablo. Small wonder the public land survey grid for most of California and all or Nevada originates here.
Looking south.
Looking west: Mount Tamalpais is on the horizon at left. Views below look northwest and north again.

North Peak of Mount Diablo
View east over the Central Valley. Views below pan from southeast to southwest.
View southwest. The base of the distant hills is the Calaveras Fault.
View west. Fog obscures San Francisco Bay. The Calaveras Fault defines the valley in the middle distance.
View northwest. Walnut Creek is the city beyond the hills.
View northwest. San Pablo bay is in the distance.
Looking northwest.

Rocks of Mount Diablo

Vertically dipping Tertiary strata on the south side of Mount Diablo.
View west from the southern slopes, showing a hogback of Tertiary rocks in the near distance.
The break in slope marks the approximate contact between Tertiary rocks and upthrust Franciscan rocks. Below are views of the Franciscan rocks.


R.W. Graymer, D.L. Jones, and E.E. Brabb, 1994, Preliminary geologic map emphasizing bedrock formations in Contra Costa County, California: A digital database, U.S. Geological Survey Open-File Report 94-622.

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Created 12 January 2006, Last Update 06 June 2020