Point Diablo, Marin Headlands

Point Diablo, Marin Headlands

by | May 18, 2022

Point Diablo extends about 600 feet (183 m) south from the Marin Headlands roughly midway between Point Bonita to the west and Lime Point to the east, about 6 miles (10 km) northwest of San Francisco and 2.7 miles (4 km) south-southwest of Sausalito, California. The point was named for being a navigational menace for ships entering or exiting the Golden Gate in fog. Marin Headlands is a peninsula forming the northern shore of the Golden Gate and named after Chief Marin of the Licatiut band of Coast Miwok, also known by his Native name Huicmuse and his baptized name Marino. These headlands are comprised of rock formations collectively called the Franciscan Complex created by the accretion of oceanic rock and sediments onto the North American continental plate during the tectonic process of subduction. The southern end of the Marin Headlands consists of rocks from a unique tectonostratigraphic terrane that is part of the Franciscan Complex consisting of pillow basalt overlain by radiolarian chert, which in turn is overlain by greywacke sandstone and shale. The basalt formed during the Early Jurassic, about 190 million years ago, at a mid-ocean ridge, and was subsequently buried by radiolaria during the terrane’s long trip across the ocean that took about 100 million years. The terrane eventually arrived at a deep ocean trench where the chert was buried by Cretaceous turbidites derived from an eroding volcanic arc. The volcanic arc was probably related to an ocean-continent subduction zone because the turbidites, which lithified into greywacke sandstone, contain minerals such as feldspar that were derived from continental rocks. This may mark the approach of the Marin oceanic terrane to the North American plate followed by partial subduction and accretion that formed the present-day headlands. The radiolarian chert suggests that the basalt formed near the equator and then was carried eastward or northeastward toward North America. The terrane entered a trench far to the south of its present position, probably somewhere around southern Mexico, and then was carried northward as much as 2500 miles (4,000 km) by right-lateral transform faulting. Point Diablo is composed of erosion-resistant serpentinite, a type of metamorphosed basalt, at the outermost tip and chert toward the base of the point.

The Coast Miwok were hunters and gatherers whose ancestors occupied the Marin Peninsula area for millennia, and about 600 historical village sites have been identified. Francis Drake provided the first documentation of the Coast Miwok from encounters over a five-week period in 1579 when he stopped to repair his ship the Golden Hind. In 1595, Sebastião R. Soromenho sailed from Manila on the San Agustin and reached the California coast between Point St. George and Trinidad Head. He then followed the coast south to Drakes Bay and was greeted by the Coast Miwok in a manner similar to that offered to Drake 16 years earlier. In 1776, the Mission San Francisco de Asis was founded and by 1817 had evangelized about 850 Coast Miwok. In 1817, Mission San Rafael was established on the Marin Peninsula but by that time the only Coast Miwok people still on their traditional lands were those on the Pacific Coast north of Point Reyes. In 1834, the mission lands were secularized following Mexico’s independence from Spain, and the Coast Miwoks were freed from the control of the Franciscan missionaries. In 1835, a Mexican land grant of 19,752 acres (7993 ha) called Rancho Saucelito was given to José Antonio Galindo by Governor José Figueroa. In 1838, Galindo was arrested for the murder of José Doroteo Peralta, and Rancho Saucelito was re-granted to William A. Richardson by Governor Juan Alvarado. Many of the remaining Coast Miwok began to live in servitude on the ranchos for land grant owners. By 1850, at the beginning of California statehood, many Coast Miwok of the Marin Peninsula were working as farm laborers on ranchos that were rapidly passing from Mexican to Euro-American ownership. In the 1890s, the first military installations were built on the Marin Headlands to prevent hostile ships from entering San Francisco Bay. The gun batteries at Kirby Cove to the east of Point Diablo and at Black Sands Beach to the west, are examples of fortifications from the pre-World War I period. During World War II, Batteries Wallace, Townsley, and 129 on Hawk Hill were built into the mountain to protect them from aerial bombardment. During the Cold War, anti-aircraft missile sites were built on the northern and southern sides of Rodeo Lagoon. Radar sites were placed atop Hawk Hill and Hill 88. At several locations, shelters were built into the hillsides to protect military personnel from nuclear, biological, or chemical weapons. In 1972, President Richard Nixon established the Golden Gate National Recreation Area and today, all military sites in the headlands are decommissioned and returned to civilian use.

Starting in 1848, the Gold Rush in California caused a dramatic increase in vessel traffic along the coast and in San Francisco Bay, and aids to navigation were desperately needed to prevent shipwrecks. In 1852, the U.S. Congress appointed a nine-member Lighthouse Board to take control of the lighthouse system from the U.S. Treasury Department. The Lighthouse Board was divided into 12 districts, with the Pacific Coast and Pacific Islands in District 12, and was immediately tasked with building a series of lighthouses on the U.S west coast and purchasing Fresnel lenses for all existing and new lighthouses. A survey team was sent to California to identify sites most in need of navigational aids. Fort Point light and Alcatraz Island light were built in 1853. In 1854, a lighthouse was built on Point Bonita on the northern shore of the Golden Gate. In 1883, a brick structure was built for the Lime Point Lighthouse. In 1906, Mile Rocks Lighthouse, about 0.4 miles from the southern shore, was completed. In 1923, the U.S. Lighthouse Service decided to build a navigational aid on Point Diablo to mark this navigational hazard. The site is on a very steep rocky headland about 1.2 miles (2 km) west of the Golden Gate Bridge. A small white shack with a pitched red roof was constructed on the sloping point 85 feet (26 m) above the water. The original structure housed two lanterns and an electric siren, for which the lightkeepers at Lime Point were responsible. A telephone and an electric line were strung on poles between Lime Point and Point Diablo allowing the lightkeepers to monitor the semi-automated station. Still, the keepers were required to travel to Point Diablo weekly to clean the light and oil the fog signal. In 2007, the navigation light was mounted on a post beside a square 1-story wood fog signal building.  Today, an array of solar panels powers the modern beacon positioned atop the shack and shows a white light 3 seconds on and 3 seconds off. The fog signal is continuously operating with a blast every 15 seconds. The station is accessible only by boat and is closed to the public. Read more here and here. Explore more of Point Diablo and Marin Headlands here:

About the background graphic

This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2022 (bottom). Each stripe represents the average global temperature for one year. The average temperature from 1971-2000 is set as the boundary between blue and red. The color scale goes from -0.7°C to +0.7°C. The data are from the UK Met Office HadCRUT4.6 dataset. 

Credit: Professor Ed Hawkins (University of Reading). Click here for more information about the #warmingstripes.

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