3.  SETTING

The weather of the San Francisco Bay area is characterized by a Mediterranean pattern of cool and mild temperatures along the coast, dry summers, and small fluctuations in seasonal temperatures.  The eastern side of San Francisco is generally warmer and drier than the western side.  East to west gradients of fog, precipitation, and temperature, coupled with the highly variable topography in the City, produce strong microclimatic effects.  San Francisco's City parks lie within the seismically active Bay Area of the Coast Ranges geomorphic province of Northern California.  The San Andreas Fault Zone is a primary feature of the regional geology.  The central portion of the City that was known as the San Miguel Hills contains Mt. Davidson, Twin Peaks, Buena Vista Park, and Mount Sutro.

All parks surveyed contain Franciscan bedrock.  Franciscan rocks consist primarily of various types of sandstone but can also include chert, shale, and conglomerate. The Barnabe-Candlestick and Candlestick-Kron-Buriburi complex soil complexs are both relatively common. The Barnabe complex is a mixture of very gravelly sandy loam and fine sandy loam.  The Candlestick-Kron-Buriburi complex is fine sandy loam, sandy loam, and gravelly loam.  Sirdrak sand formed on coastal dunes and is now found at Golden Gate Park, Buena Vista Park, and Golden Gate Heights, among others. The southern area around Lake Merced is underlain by wind-deposited sandstones from earlier in the Pleistocene than the northern dune system.

Erosion is a significant physical process affecting Significant Natural Resource Areas and the plant and animal communities contained in them.  Although many erosion areas do not appear active year round because of the seasonal nature of water input, such problems persist and are exacerbated by steep slopes, road cuts, other unnatural surfaces, and heavy year-round foot traffic at many of the parks.