 Although most of the watershed is located in Irvine, it also includes parts of the incorporated cities of Aliso Viejo, Laguna Hills, Laguna Woods, Lake Forest, Orange, Santa Ana, and Tustin.The watershed forms a flat, highly urbanized basin which is bounded on the north by the Loma Ridge, the "front range" of the Santa Ana Mountains, which separates it from the valley of Santiago Creek.Loma Ridge elevations range from .