The physical geography of Santa Clara County, situated between the Santa Cruz Mountains to the west and the Diablo Mountain Range to the east, was formed quite recently in geological history. Santa Clara Valley was created by the sudden growth of the Santa Cruz Mountains and the Diablo Mountain Range, during the later Cenozoic era. This was a period of intense mountain building in California when the folding and thrusting of the earth's crust, combined with active volcanism, gave shape to the present state of California. Hence, Santa Clara Valley is a structural valley, created by mountain building, as opposed to an erosional valley, or one which has undergone the wearing away of the earth's surface by natural agents. The underlying geology of the Santa Cruz Mountains was also formed by the sediment of the ancient seas, where marine shale points to Miocene origin. Today one can still find evidence of this in the Santa Cruz Mountains, where shark's teeth and the remains of maritime life are still found as high as Scott's Valley, a city nestled in the mountains.
The Santa Cruz Mountains and Diablo Mountain Range created a sheltered valley. Located south of the San Francisco Bay, Santa Clara Valley offered shelter from the cold, damp climate of the San Francisco region and coastal areas west of the Santa Cruz Mountains, and was no doubt inviting to the first human inhabitants. Historically, the Tamien-speaking Ohlone Indians were the first documented inhabitants of the Santa Clara Valley region, although the oak lined hills and valley undoubtedly had known earlier Indian inhabitants and migrations, now lost to history and prehistory. Archeological discoveries place Ohlone Indian settlements in the region as early as 8000 BC.