Manhattan Project (1941-46): Research at sites including Los Alamos, N.M., yield first atomic weapon.

Trinity Test (1945): First atomic bomb detonated in Alamogordo, N.M. Later, continued bomb testing above ground in Nevada is believed to have caused illness among a group known as the Downwinders, who grew up in places where fallout rained down in the 1940s and '50s, including southern Utah.

Japan bombed (1945): Enola Gay crew, which drops the first atomic bomb on Japan, starts training in 1943 in Wendover, Utah.

Uranium prospecting (1946-1959): More than 300,000 claims in Moab area file for uranium, spurred by the need for nuclear weapons material.

Uranium boom (1955): At least 800 mines across the Colorado Plateau in operation.

End of boom (mid-1960s): Federal government stops purchasing uranium due to large stockpile.

Second uranium boom (1970s): Uranium mining in southern Utah sees a resurgence to provide fuel for nuclear power plants.

Research reactor (1975): University of Utah is licensed to operate small research reactor.

Proposed permanent repository (1984): Congress tells Department of Energy to study Yucca Mountain, Nev., as one of three candidate sites for first permanent geological repository for high-level nuclear waste.

First commercial reactor in Intermountain West (1985): Palo Verde 1 in Arizona becomes first of three nuclear reactors at a site near Phoenix. These are the only three commercial nuclear plants in the region. No others proposed in the region at this time.

Repository planning begins (2002): Department of Energy given permission to begin establishing permanent repository at Yucca Mountain. So far, authorization has not been given to begin building. Groups in Utah oppose it, citing the possibility of dangerous waste being transported through the state on railways or highways.

Temporary waste storage proposal (2006): Private group proposes temporarily storing high-level nuclear waste at Skull Valley in Utah's west desert until Yucca Mountain is operational.

Sources: University of Utah, Division of State History, U.S. Department of Energy