Testing of devices for defense and for peaceful uses of nuclear explosives is conducted here. The nation's principal nuclear explosives testing laboratory is located within this 1,350 square mile, geologically complex area in the isolated valleys of Jackass, Yucca, and Frenchman Flats. Selected as an on-continent test site in 1950, the first test took place on Frenchman Flat in January 1951. Archeological studies of the area have revealed continuous occupation by prehistoric man from about 9,500 years ago. Several prehistoric cultures are represented. The last aboriginal group to occupy the site was the Southern Paiute, who foraged plant foods in season and occupied the area until the coming of the pioneers.