Today in 1968, the United States conducted Schooner, a Project Plowshare experiment in which a 30-kiloton device was exploded 355 feet under the Nevada Test Site to study nuclear excavation techniques. This was the last US nuclear test to deliberately reach with the atmosphere. 
Here is restored official footage of the Schooner explosion breaching the surface and the early formation of the resulting highly-radioactive dust cloud:
And here is a short official (but silent) film about the preparations for and execution of the Schooner test, including multiple views of the explosion and the very large dust cloud from the ground and the air.
To demonstrate the power of the nuclear explosion, this film superimposes a standard football field inside the 426-foot-wide, 208-foot-deep crater, before showing the entire Rose Bowl could fit inside.
Here are the estimated trajectories for Schooner’s radioactive fallout cloud at different altitudes for several days after the test:
** to deliberately reach the atmosphere **
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