The Tejon Formation was deposited from early to late Eocene time in a variety of shallow-to-deep marine environments along the western margin of the North American continent. It crops out in east-west-trending mountain ranges along the southern margin of the Great Valley of California. These ranges offer the only exposures of Eocene rocks underlying the Valley on the north. On the basis of new megafaunal data, deposition of the Tejon commenced in the early Eocene with the Uvas Conglomerate Member, a shallow-marine basal conglomerate and sandstone that rests unconformably on pre-Tertiary crystalline basement rocks. The Uvas records a slow transgression of the sea from west to east. It grades upward into the Liveoak Shale Member, consisting of shales, siltstones, and thinly bedded, fine-grained sandstones. The Liveoak was deposited seaward of the Uvas in middle and late Eocene time; it grades laterally eastward into shallow-marine sandstones and conglomerates and laterally westward into hemipelagic foraminiferal shales. The Metralla Sandstone Member was deposited by the westward-retreating, late Eocene sea. It is a locally conglomeratic, shallow-marine sandstone that overlies the Uvas in the easternmost part of the area, and the Liveoak in all other areas. It grades laterally westward into thinly interbedded, fine-grained sandstones and shales deposited in deeper water, and farther west into the hemipelagic shale facies of the Liveoak. The Reed Canyon Siltstone Member, the uppermost member of the Tejon Formation, discontinuously overlies the Metralla and wa deposited during the late Eocene in shallow-marine environments, including probably lagoonal areas behind barrier islands. Thus, the Tejon Formation records an advancing and retreating shoreline across a narrow continental shelf, bordered on the east by alluvial plains and on the west by an irregular continental borderland containing deep-sea basins in which submarine fans were being deposited.

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