A small arroyo behind my house leads eventually to Mescal Wash and, from there, through ever widening washes until eventually reaching the Santa Cruz River, about forty miles to the west. Also near my house, there is this low ridge just a few hundred yards to the east. On the other side of its low crest is an arroyo called Cornfield Wash, and it leads a scant few miles to the nearby San Pedro River. That means that this modest ridge line marks a divide between two major river valleys in southern Arizona; the San Pedro drainage to the east, and the Santa Cruz to the west.