Extract of a map dating back to 1864, showing the two oval-shaped marshes (mispelled "sienega" for cienaga in Spanish) along the southwestern edge, which gave its present name to the Ojos Negros valley. These marshes have now all but disappeared due to groundwater depletion (Zárate Archives, Ensenada, Baja California, as cited in Minnich and Franco, 1998).