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It is overlain by the Vasquez series which crops out over a wide area,

and comprises interlayered fanglomerates and volcanic rocks. Where

the Martinez formation has been removed by erosion prior to the

deposition of the Vasquez beds, the Vasquez series rests on the pre-

Tertiary crystalline rocks. This unit is of doubtful Oligocene age,

and has a maximum known thickness of nearly 16, 000 feet: The Vasquez

beds were deposited in three basins separated by ridges. Late in

Vasquez time, these ridges were buried by thick alluvial fans built

northward from the San Gabriel Mountains, and the basins thus

coalesced into a single broad alluvial apron.

The upper Lower Miocene Tick Canyon formation and the

Upper Miocene Mint Canyon formation, which lie above the Vasquez

series, also represent nonmarine deposition of dominantly coarse-

grained sedimentary material. These units are widespread in the

western part of the Soledad basin. Sandstone and siltstone of the

''Modelo" formation rest unconformably on the Mint Canyon beds, and

reflect an eastward encroachment of marine waters over a part of the

basin in late Miocene time. West of the map area, the marine Plio-

cene Pico formation and the nonmarine Plio-Pleistocene Saugus forma-

tion, which grades westward into a marine facies, overlie the older

rocks. Terrace deposits of late Pleistocene age are common over

much of the area. Recent alluvium is present in all of the major

valley bottoms and locally in some of the minor valleys.