Tenmile Wash begins east of Ajo, Arizona.
At this point a water divide occurs with the drainage south actually turning back northwest as part of the San Cristobal drainage through the Growler Valley (and is the north end of the Valley of the Ajo).
East and north of Ajo, Tenmile Wash flows northwest through the Childs Valley, on its eastern edge, as the west side of the Childs is drained by the Daniels Wash, again flowing into the San Cristobal drainage to the west.
At the downstream north end, Tenmile Wash traverses the western Sentinel Plain and enters the Park Valley through the 5-mile-long (8 km) Canyon Diablo; the watercourse then forms its own watercourse flowing southwestwards paralleling the Gila River to the north.
Midway Wash is the eastern portion of the Tenmile Wash drainage; it also drains northwesterly into regions of the southern and central Sentinel Plain.