In 1835, the newly annexed state of California sees an influx of American settlers moving West along the El Camino Real; these Americanos are perceived as a threat to the rancheros of the Spanish dons. Among the rancheros are Gabby and his niece Jean, who are leading a wagon train to meet their friend, Roy Rogers. Roy, a trusted hand on the ranch of Don Jose, is returning from a cattle drive with Carlos, son of the don, when he decides to ride ahead to the ranch, leaving Carlos behind with the wagon bearing the proceeds of the sale. On the ridge above the wagon awaits Suguaro, the half-breed foreman of Don Jose's ranch, who has led a band of "gringo" bandits to prey upon Carlos and the gold. When the bandits shoot Carlos and steal his gold, the clever Suguaro accuses the settlers of the crime, and when Roy protests, Don Jose banishes him from the ranch. After Roy joins Gabby and the wagons, he follows Suguaro to the bandits' cave hideout, but the clever Suguaro escapes Roy's trap and accuses Roy and Gabby of stealing the gold. When Don Jose orders the Americanos imprisoned, Jean pleads with the don to listen to their explanation. The don agrees, but before he can free Roy, Suguaro shoots him and frames Roy for the murder. Aided by Rita, the don's daughter, Roy and Gabby escape, but Carlos refuses to abandon the search for his father's killer. One night, Carlos follows Rita to Roy's grotto hideout, and Roy succeeds in convincing him that it was Suguaro who murdered his father. Together, they plan a massive cattle drive to tempt the bandits, and the trap works as Roy, Carlos and their men ambush Suguaro and their band. Thus vindicated, Roy rides off to San Diego with Jean and the wagon train.