Poster with craters

A publicity poster left at the Nevada National Security Site showcases the results of the many underground nuclear tests done there. Each of the craters seen in the poster is the result of one of the tests.

In an underground test, a hole was drilled straight down, from a few hundred to a couple thousand feet deep. A rack of diagnostic equiopment along with the weapon was dropped into the shaft, and then the hole was plugged with various materials so that no radiation would rise above the surface.

The detonation would initially vaporize the dirt and rock, but as it cooled, it would subside, causing craters like these.