The name Newberry Basin is given to an area east of Barstow underlain by a large thickness of relatively unconsolidated continental sedimentary rocks which lie upon Miocene or older rocks. The areal limits of the basin are roughly those given by Buwalda (1914) as that for Lake Manix and represent a present-day tectonically negative area. The mountain ranges bordering the basin have been structurally positive since at least the post-Miocene orogeny. Very large thicknesses of extrusive volcanic and continental sedimentary rocks overlying pre-Tertiary "basement rocks" compose most of the mountain masses.

The post-Miocene sedimentary rocks filling the upper part of the basin are given the name Newberry formation and several facies of the formation can be recognized. The prominently exposed Lake Manix green clay represents deposition in a relatively long-lived Pleistocene desert lake. Coyote Lake, a present-day playa, had a short-lived period of Pleistocene pluvial sedimentation. A widespread sand unit is newly recognized as a deltaic facies of Lake Manix. The marginal facies deposited on the flanks of the basin are represented by fan deposits. Lateral gradations of all these facies can be seen in outcrop. Underlying this upper unit of Lake Manix time are older fluviatile and fan deposits.

The unit proposed as the Yermo formation by McCulloh (in press) composes the lower part of the Newberry Basin fill. Only the marginal facies (sand and gravel) of the Yermo formation are exposed for certain in outcrop; however, fine-grained facies are suspected to exist in the basin subsurface. Additional information from well data allows an interpretation of continual filling of the basin with sediments since possibly Pliocene time. Early recognition of the nature of Newberry Basin sedimentation was made by Thompson (1929). Interruptions of any magnitude in the deposition have occurred along the margins of the basin only and represent structural adjustments of the "basement rocks."

Alvord Mountain has a history of renewed uplift since the beginning of Yermo deposition. Several major faults cross or border the basin. Recent movements have occurred along the Manix fault zone and the Cave (Afton) Canyon fault system. The latter caused damming of the Pleistocene Mojave River and formed the several stages of Lake Manix and possibly earlier pluvial lakes.

Hydrocarbons are found in minute quantities in Miocene fresh-water shale concretions in the Calico Mountains and several test wells have reported oil and gas in the Newberry Basin. Modern knowledge of the origin of petroleum and the understanding of the environments of sedimentation in this region allow for reasonable explanations, but do not predict significant occurrences of oil or gas. Saline minerals, primarily borates, are being extensively sought in the Mojave Desert region. Additional occurrences in the Newberry Basin area besides those in the Calico Mountains are evaluated in the light of the present study. The possibility of buried borate-bearing beds of the Miocene Barstow formation is considered to warrant further exploration.

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