Complex sentence: In 1860, the Carillos sold Rancho Mission Vieja de la Purisma to the More brothers, who were the largest landowner in Santa Barbara County (which at the time included all of present day Ventura County).
Split into simpler sentences: In 1860, the Carillos sold Rancho Mission Vieja de la Purisma to the More brothers. By 1860, the More brothers were the largest landowner in Santa Barbara County (which at the time included all of present day Ventura County).