Jackass Flats is a shallow alluvial basin located in the southwest portion of the Nevada National Security Site in Nye County, Nevada. The area lies east of Yucca Mountain, south of the Calico Hills and Shoshone Mountain and northwest of Skull Mountain. The valley drains to the southwest via the Tonopah and Fortymile washes into the Amargosa Valley across US Route 95 at Amargosa Valley. The "flat" covers an area of approximately and ranges in elevation from about just north of US 95 to at the mountain bases to the north and east.