The Valley and range sequence-Southern Yuma County is a 3-Valley sequence of NW–by–SE trending block faulted valleys and mountains. About eleven major mountain ranges connect to each other in four, (mostly parallel), mountain sequences. This regional parallel valley-mountain sequence ends at the Gila River valley at the north; to the south, it extends to the Gran Desierto de Altar of northwestern Mexico; the sequence is a remnant of the Basin and Range system.