Much like the other nearby lakes in the southeast portion of the Point Reyes peninsula, Bass Lake occupies a natural synclinal depression formed behind blocks of rock displaced by landslides within the past 10,000 years. The depressions forming Crystal, Pelican and Bass lakes appear to have been caused by the Double Point Slide, which covers an area of about. The rocks involved in the landslide are shale, chert and sandstone, some similar to Miocene rocks of the Monterey Formation and others to Pliocene rocks from the Central Coast Ranges. The process that caused these slides is ongoing, with several nearby slides caused by the 1906 San Francisco earthquake and others happening as recently as 1956.
Ecology
The lake is within the Southern Inverness Ridge region of the Point Reyes National Seashore, in an area of coastal scrub and grassland. In this coastal zone there are open stands of coyote brush, often with native grasses such as California oatgrass and purple needlegrass. The other dominant plants in this ecosystem are California sage brush, black sage, sticky monkeyflower, poison oak, California coffeeberry and tree lupine. Around Bass Lake and the neighboring lakes are thick growths of willow In the lake margins there is common tule, California bulrush, cat-tail and sedges. The lake has been stocked with warm-water game fish. Research in 1976 found that the lake supported a range of phytoplankton from the genera Anabaena, Cryptomonas, Cymbella, Fragilaria, Oocystis, Schroederia, Sphaerocystis and Staurastrum, as well as the species Ceratium hirundinella, Elakatothrix gelatinosa and Pseudokephrion conicum. On the slopes above the coastal lakes, the flora is characterized by stands of Douglas fir. Bass Lake is inland from the Double Point Area of Special Biological Significance, established in 1974 primarily to protect the large population of harbor seals that raise pups on the beach between April and June each year.
History
Prior to geological research in the 1960s that revealed the many pre-historic landslides, the area was considered to be sufficiently stable for the U.S. Army to construct an underground artillery control facility within the North Point headland directly west of Pelican Lake in 1944. These concrete structures were filled in by the National Park Service after it assumed control of the area, but they could be exposed by future landslides. The barracks for this facility were located near Bass Lake.
