San Bruno Mountain
Map SatelliteAn "island" in the midst of urban development, San Bruno Mountain preserves a flora and fauna typical of the northern San Francisco Peninsula before the advent of urbanization. It also supports a number of rare and endangered species.
Three plant communities are found here, grassland, coastal scrub and coastal foothill woodland, with the first covering the greatest portion. Coastal scrub is found primarily in the canyons and ravines. The coastal woodland occurs in a few canyons. A total of 384 native vascular plants (plus 158 introduced species) have been reported from the mountain. Six of the natives are rare. Arctostaphylos glandulosa X Arctostaphylos uva-ursi is known only from this area and Arctostaphylos montaraensis from only one other site. Other rare species are Arabis blepharophylla, Erysimum franciscanum, Triphysaria floribunda, and Tanacetum camphoratum. The California pipe vine, Aristolochia californica, reaches its southernmost distribution here.
The mountain serves as a refugia for numerous animals. Reports of the existence of the endangered San Francisco garter snake, Thamnophis sirtalis tetrataenia, in the area have not been verified. The lycaenid butterfly, Callophrys fotis bayensis, is known only from this area.
A graywacke of the Francisco Formation, laid down in the late Cretaceous, comprises the bulk of the mountain. This dark, greenish-gray graywacke is exposed on the ridge crests on some of the steep canyon sides. There are several small serpentine outcrops.
Integrity: There are roads, a working quarry, abandoned gold and zinc mines, radio towers, etc., that have disturbed parts of the area. However, extensive acreage is relatively undisturbed. Development of a part of the area is pending.
Use: Private
Ref: McClintock, Elizabeth, W. Knight and N. Fahy. 1968. A Flora of the San Bruno Mountains, San Mateo County, California. Proc. Calif. Acad. of Sci. 32 (20), p. 587-677.
May 1975
Inventory of California Natural Areas
Revision © 2009 Steven Louis Hartman
