July 6, 1962 - The mightiest nuclear blast within the U.S. and the first known detonation of any hydrogen type of explosive in this country was set off underground today. It tore a great open-faced crater in the desert floor at the Nevada test site. The thermonuclear blast was the first in a concentrated series of atomic tests. It is scheduled to be followed tomorrow by the first atmospheric nuclear shots here in four years. Today’s explosion created a crater about 300 feet deep and a third of a mile wide in rocky, sandy soil. A flash of light preceded the spray of dirt and rock that shot some 7,000 feet high, witnesses estimated. A huge, dirty cloud rose into the clear sky. The cloud — visible 65 miles to the southeast in Las Vegas — first had the shape of a stemless mushroom. Then it took the form of a stack of immense, inflated rubber tubes.