Point Diablo is 1.6 miles (2.6 km) north-northeast of Point Bonita and 1.2 miles (1.9 km) south-southwest of Lime Point in the Marin Headlands on the northern side of the Golden Gate, California. The point protrudes dangerously into navigable waters that are often foggy.
In 1923 the U.S. Lighthouse Service built a small white shack with a pitched red roof on the sloping point about 80 feet (24 m) above sea level. The structure housed two lens lanterns and an electric siren, for which the light keepers at Lime Point were responsible. Telephone and electric lines were strung on poles to the point allowing the Lime Point keepers to listen-in on the semi-automated station. Still, the keepers were required to travel to Point Diablo weekly to clean the light and oil the fog signal. Today, an array of solar panels powers the beacon that flashes a light every six seconds.
The distinctive red rocks of the Marin Headlands are an oceanic geological sequence that includes basaltic crust covered by red radiolarian chert, with overlying continental-derived sandstone. Fossils in these rocks indicate that the chert was deposited from about 200 million to 100 million years ago and the sandstone between 100 and 90 million years ago. Tropical fossils and paleomagnetic evidence indicate that the rock originated in the open ocean of the central Pacific near the equator. It then moved northeastward with the oceanic plate towards the North American Plate, finally colliding with North America at the latitude of today’s Mexico. After this oceanic fragment became attached to the North American margin, rather than being subducted under it, lateral faulting transported it northward along the western edge of the continent. Finally, San Andreas related transform faulting moved it farther up the coast to the Bay area and rotated the Marin Headlands block into the position found today. Read more here and here. Explore more of Point Diablo here: