The Point Bonita Lighthouse was built in 1855 to mark the entrance of the San Francisco Bay for Sailors coming from the South. The Lighthouse is currently maintained by the U.S. Coast Guard today as a navigational aid to assist captians and sailors safely through the tricky and sometimes dangerous waters at the mouth of the Bay. Modern navigation charts illustrate lighthouses with a number next to them indicating their unique pattern of fog horn blasts and light patterns. The Point Bonita Lighhouse sends out two sound blasts in heavy fog every 30 seconds. Sir Francis Drake, in his orginal exploration of the Northern California coast, missed the San Francisco Bay because of heavy fog. Fog makes sound travel further, and the denser the fog, the further it travels. The foghorns are a distuingishing sound guiding safe passage for ships before GPS and Radar.

The Point Bonita Lighthouse employs a Fresnel lens, a type of articulated lens invented by French physicist Augustin Fresenl in 1822. The Fresnel lens is a series of ground glass prisms arranged around a light source to focus the outgoing light in one direction by refracting and reflecting light through the lenses. Fundamentally what this means is that a light source is focused into one direction and one beam which can make the light is stronger and brighter up to 70%. Point Bonita's Fresnel Lens system can send it's light beam 18 miles accross the water in clear weather. The Point Bonita light pattern is on for three seconds and off for one. The Fresnel Lens was very expensive in it's time and the Point Bonita Lighthouse only has the Fresnel Lens on the west side of the Lighthouse.

The Lighthouse is on a geological formation called Pillows Basalt which is a black volcanic formation that is extremely hard and durable. The durability of Pillows Basalt is why Point Bonita and the Lighthouse survives pounding storms, earthquakes and seas. Surrounding cliffs are sedimentary and have eroded from storms and tides. Carnelian, an orange coral colored semi-precsious stone, formed in pockets of the Pillows Basalt and small egg like stones polished by the seas can be found on the nearby beaches.

The Point Bonita Lighthouse is part of the Golden Gate National Recreation Area, the largest urban national park in the United States. The park is an undeveloped swath of land that extends north providing trails for recreation, habitats for wild life and preserving the natural landscape. The views of scenic Northern California Coast preserved by the GGNRA park from the Pacific Ocean are dramatic and breath taking.

The Point Bonita Light house is one of America's historical lighthouses and worth exploring. For more information on the Lighthouse, visit www.nps.gov/goga/mahe/pobo. or contact:

Marin Headlands Visitor center Bldg. 948
For Barry Sausalito, California, 94965
Phone: (415) 331-1540


Other Bay Area Lighthouses:
click on the Lighthouse name to learn more.

• ALCATRAZ ISLAND LIGHT (1909)
• EAST BROTHER ISLAND LIGHT (1874)
• FARALLON ISLAND LIGHT (1855)
• FORT POINT LIGHT (1853)
• LIME POINT LIGHT (1883)
• OAKLAND HARBOR LIGHT (1903) (currently relocated and used as a restaurant)
• SOUTHAMPTON SHOALS LIGHT (1905)
• YERBA BUENA ISLAND (GOAT ISLAND) LIGHT (1875)
• CARQUINEZ STRAIT LIGHT (1910)
• POINT BLUNT LIGHT (1956)
• POINT MONTARA LIGHT (1928)

• PIGEON POINT LIGHT (1872)
• POINT SUR LIGHT (1889)

• POINT REYES LIGHT (1870)
• CAPE MENDOCINO LIGHT (OLD) (1868)