San Bruno Mountain rises above the south edge of San Francisco Bay as a distinct fault-block horst on the northern San Francisco Peninsula, separate from the Santa Cruz Mountains both geographically and geologically. Its ridge, much of it protected in state park and ecological reserve lands, preserves one of the peninsula’s largest surviving remnants of original grassland and scrub. The mountain’s Franciscan Formation rocks, windy exposed setting, and fog-influenced climate support rare habitats with endangered butterflies and uncommon native plants. It also has deep human history, from the Ramaytush Ohlone hamlet of Siplichiquin to the urban growth that later reshaped its margins.

Photo: Wikipedia · Public domain

Photo: Wikipedia · Public domain

Photo: Wikipedia · Public domain