The Moreno adobe, the older of the two found on the Reserve, was constructed in 1845 when Juan Moreno moved 100 head of cattle to the Plateau. According to a map dated 1846, the structure originally consisted of four rooms and sat upon 48,000 acres granted to Senor Moreno by Pio Pico; the last Mexican governor of the territory of California. Three rooms washed away in a heavy winter storm in 1884.
In 1855, the US Attorney General challenged his right to the Plateau land. Unable to financially pursue the matter in court, Moreno sold his Santa Rosa Rancho to Augustin Machado on August 17, 1855. The price was $1,000 plus $500 worth of livestock.
The Machado adobe is believed to have been built that same year for use by ranch hands. Juan Machado inherited the land of the Plateau from his father in 1865. The Machados title to the land was not finalized until 1872.
The Santa Rosa Rancho was sold to a group of British businessmen in 1876 for one dollar an acre. One of the men, John Dear, bought out his partners interests in the Rancho on August 15, 1878 two years after his son Parker Dear was already living on the ranch. Living in a two-story house of 14 rooms, Parker Dear used the adobes as quarters for ranch hands. The large Dear home burned in a human-started fire in 1974. Following flood events that twice destroyed the railroad connection with San Diego, Parker Dear was forced to put the ranch into receivership in 1894.
Walter Vail, already a successful ranch owner in Arizona, bought the Santa Rosa Rancho in 1904. For 60 years under Vail family and Vail Corporation ownership, the Machado adobe was used as a bunkhouse, and the remaining room of the Moreno adobe was used for a time as a sort of jail house for drunken cowboys.
On December 4, 1964, the Vail Ranch was sold to Kaiser Steel for $21 million. Much of the ranch was leased for cattle grazing as the Machado adobe continued as a bunkhouse and the Moreno was used as a tack room for horse equipment.
In 1984, The Nature Conservancy purchased 3,100 acres of land on the Santa Rosa Plateau, which included the Moreno and Machado adobes – Riverside County’s oldest standing structures.