Camp Reynolds, Sausalito in distance.
View of Golden Gate from Camp Reynolds, century plants (maguey) in foreground.
View of Golden Gate from Camp Reynolds, pillow basalt of north beach in foreground.
Pillow basalt forms from lava extruded underwater and is typical of eruptions at mid-ocean ridges where oceanic crust forms. The smoother-surfaced rock in this picture is chert, made from siliceous plankton that settled on the seafloor after the lava cooled.
Blueschist in seacliffs at the south end of Camp Reynolds beach.
Blueschist in seacliffs at the south end of Camp Reynolds beach.
Blueschist in seacliffs at the south end of Camp Reynolds beach.
Blueschist is colored blue by the mineral glaucophane, a mineral that forms at low temperatures but high pressures. It is characteristic of subduction zones, because the original sediments are carried deep into the Earth in too short a time to reach temperatures typical of such depths.
At Perle Beach, Late Pleistocene (end of the last ice age) sand and gravel of the Colma Formation are on top of the Cretaceous-age melange typical of the island.
Blueschist and serpentine boulders near the south end of Perle Beach
Brown stilpnomelane-bearing schist interlayered with blue-gray glaucophane-bearing quartz-rich rock (formerly clay / chert interlayers?) near the south end of Perle Beach. Boulder is about 3 foot square. - Streetcar to Subduction, p. 51.
Serpentine is a green, slippery rock that formed from the interaction of newly formed oceanic mantle and seawater. It can be scraped off together with overlying basalt of the oceanic crust when the crust reaches a subduction zone. View of San Francisco from Angel Island Serpentine quarry.
View of Mt. Tamalpais and the Tiburon Peninsula from the Mt. Livermore, the highest point on Angel Island.