First mentioned in the journals of the Anza expedition of 1775–1776 and named for St. Margaret of Antioch, this site was originally established by the padres from Mission San Luis Rey and built by Native American labor. By 1841, some 13,800 acres of mission land was transferred by the Mexican government to Andres Pico and his brother Pio, the last Mexican governor of Alta California, who transformed it into a ranch. Eventually purchased by Richard O’Neill and James Flood in 1882, the site became the center of a large cattle-ranching operation until 1942, when 9,000 acres were acquired by the U.S. government for a Marine Corps training station. The original, single-story, eighteen-room ranch house, constructed ca. 1827, continues to serve as quarters for Camp Pendleton’ commanding officers. Within the ranch house, a verandah encircles a square internal courtyard with a central fountain surrounded by flowering herbaceous plants. Planting beds, with roses and other flowering shrubs, are located at the four corners of the courtyard.
Encompassing little more than twenty acres within a valley, the complex also contains a bunk house and small chapel (both previously part of a winery, ca.1810). Bounded by the large Marine Corps Air Station Camp Pendleton to the southwest and a four-acre corral to the northwest, the site’s extensive sloping lawns are interspersed with sweet-olive hedgerows, cacti, palms and Engelmann Oaks. The complex was added to the National Register of Historic Places in 1971.