Structure of the continental shelf west of San Francisco, California

Journal of Research of the U. S. Geological Survey, 1975, volume 3, issue 5

“…The observations reported here indicate that, at least in the vicinity of Pescadero, this tilting is still active. The evidence presented suggests no particular cause for the tilting, but it may be related to movement on the San Gregorio fault, a branch of the San Andreas fault system that passes through the area (Cooper, 1971, and fig. 1).…”

California State Waters Map Series — Offshore of San Francisco, California

“…1, 3 on sheet 8; fig. 1 on sheet 9; Cooper, 1973;Bruns and others, 2002;Ryan and others, 2008). This graben (about 7 km long and 2.5 km wide) is bounded to the west by the San Gregorio Fault Zone (eastern strand) and Bolinas shelf, and to the east by the Golden Gate Fault and the Marin shelf.…”

Geohydrology, water quality, and water budgets of Golden Gate Park and the Lake Merced area in the western part of San Francisco, California

“…Although the fault offsets Pliocene and Pleistocene sediments which may be equivalent to the Merced and Colma Formations (Cooper, 1973, p. 43-44), its effect on ground-water flow and the hydraulic connection between the ocean and the ground-water basin is unknown. Offshore seismic reflection profiles also indicate the occurrence of moderate folding and numerous small offsets in addition to the discontinuities associated with the San Andreas and other major faults (Cooper, 1973). These smaller features may affect ground-water flow and might also occur undetected in onshore areas.…”

“…Norm of Lake Merced, the Merced Formation is overlain by the Colma Formation, but it is thought to extend continuously to outcrops along the coast of Marin County, 10 to 30 mi farther north (Schlocker, 1974, p. 67). Seismic reflection profiles indicate that the Merced Formation may extend offshore past the San Andreas fault an additional 5 to 6 mi to the Pilarcitos fault (Cooper, 1973). The Merced Formation does not crop out along the eastern side of the ground-water basin, but the formation is thought to extend beneath the Colma Formation at least as far east as the San Bruno fault (pi.…”

“…This hypothesis has been asserted by some geologists (Lawson, 1895;Edward Clifton, U.S. Geological Survey, oral commun., 1988), but another study showed the formation on both sides of the fault (Kirker, Chapman, and Associates and Todd, 1972). The apparent offshore extent of the Merced Formation also includes large areas on both sides of the projected fault trace (Cooper, 1973). In the Lake Merced area, an extensive layer of clay or silty clay about 40 ft thick at an altitude between 40 and 200 ft below sea level is evident in borehole logs on both sides of the fault.…”