according to a Wikipedia entry titled  Sedan_(nuclear_test), Sedan was a nuclear weapons  

testing project conducted by the United States  on July 6, 1962, as part of Operation Plowshare,  

a program to investigate the use of nuclear  weapons for peaceful purposes. In this test,  

A shaft was drilled into the floor of the  Nevada desert, approximately 200 meters,  

and then a roughly 100-kiloton thermonuclear  device was lowered into the shaft and detonated.  

The nuclear explosion produced a crater about the  size of a small mountain, measuring 400 meters  

in diameter and 100 meters deep. The crater was  created in sand-filled alluvial deposits though,  

not on a mountain. If the test had been conducted  in a mountain, the results may have been different