Santa Nella began as the site of Rancho de Centinela (Sentinel Ranch) first established by pioneering stockmen from San Juan Bautista and Monterey as place to raise horses in 1810. The former Centinela Adobe, a one-story adobe built as living quarters for the ranch was located on the El Camino Viejo a Los Ángeles about 3 miles downstream from the site of the later San Luis Adobe (now under the San Luis Reservoir), at the east end of the Pacheco Pass road, situated on the south bank of Arroyo de San Luis Gonzaga. The escape of many of the horses into the valley and subsequent Indian hostilities made the enterprise a failure.