The vast majority of nuclear tests at the Nevada Test Site never formed mushroom clouds. They were conducted underground—828 tests over 35 years—and these too left material for archaeologist Colleen Beck and her team at the Desert Research Institute (DRI) to study. Yucca Flat, where the largest number of nuclear detonations at the Test Site took place, is pockmarked with craters. Underground nuclear explosions vaporize surrounding rock and create a cavity that may then collapse, leaving a feature such as Bilby Crater. Eighty feet deep and a third of a mile across, the crater was created by a 1963 explosion in Operation Niblick. Most of the underground tests were related specifically to weapons development and the impact of nuclear explosions on military hardware.

The Test Site’s most famous crater, Sedan, 1,280 feet wide and 320 feet deep, was formed in 1962 by a 104-kiloton explosion in Operation Storax. Unlike Bilby, this detonation was not meant to stay underground; it was specifically designed to create a massive crater. It was the largest explosion in what is known as the Plowshare Program (30 nuclear tests across 11 operations), which examined the potential for using nuclear devices in excavation (for canals, harbors, railroad cuts, and other engineering projects), chemical manufacture, prospecting, and the extraction of natural gas from geological formations. Sedan was intended to demonstrate the feasibility of using nuclear bombs to excavate a new Panama Canal. However, public concern about the use of nuclear devices for such projects, along with other factors, led to Plowshare’s quiet end in the mid-1970s.

Deep underground tests, even those that didn’t leave craters like Bilby, left other features for the DRI to document. Some underground test sites have tunnel complexes through which weapons and instruments were moved into place. The DRI has examined some of these tunnel complexes in the Rainier Mesa area, where tunnels had been bored horizontally into the rock. Access to the miles of tunnels, some of which were used for multiple tests, is prohibited, but outside there are portal areas, vent holes, muck piles, and rail lines, all of which yield their own historical information. “We knew nothing about how a tunnel test worked, and most people still don’t,” says Beck. From evidence collected outside the tunnels, DRI researchers have already discovered much about how the tunnel networks were excavated and how they grew increasingly complex over time.