Fort Tejon is located in the Grapevine Canyon, the main route between California's great central valley and Southern California. The fort was established to protect and control the Indians who were living on the Sebastian Indians Reservation, and to protect both the Indians and white settlers from raids by the wide-ranging and rather warlike Paiutes, Chemeheui, Mojave, and other Indian groups of the desert regions to the south east. Fort Tejon was first garrisoned by the United States Army on August 10, 1854 and was abandoned ten years later on September 11, 1864.

The Native Americans who lived in this area prior to the establishment of Fort Tejon are generally referred to as the Emigdiano. They were an inland group of the Chumash people who lived along the Santa Barbara channel coastline. Unlike their coastal relatives, however, the Emigdiano avoided contact with European explorers and settlers, and were never brought into one of the missions or even incorporated into the Sebastian Indian Reservation. One of their villages was located at Tecuya Creek, north of Castac Lake. Another village, Sasau, was on the north shore of the lake, while a third and still larger village, Lapau, was located at the bottom of Grapevine Canyon. once Fort Tejon was established, the Emigdiano often worked as independent contractors for the army, providing guides for bear hunts and delivering fresh fruits from their fields for sale in officers row.