In 1993, archeologist Mark Hylkema documented eight different Native American sites on the Andresen Ranch along the lower North Fork Pacheco Creek, dating from 1000 B.C. to 500 A.D. These included multiple human burials, both adult and juvenile. He concluded that the interior of the Diablo Range north of Pacheco Pass was extensively occupied. Although Central Valley Yokuts may have utilized this area, archeologist E. Breck Parkman, who studied sites along upper North Fork Pacheco Creek, summarized evidence that the primary occupants were Ohlone, of the Tomoi, Locobo, and Cobo Ohlone peoples. These peoples were removed to Missions Santa Clara and Santa Cruz between 1800 and 1808.