Yucca Mountain, at some point before the Great War, became a nuclear waste repository where spent fuel rods and high level nuclear waste was dumped and locked away from public harm. After the Great War, Yucca became abandoned by humans and its highly radioactive contents left unchecked and left to fester for hundreds of years. No good prospector with any wits dares to enter Yucca without a good radiation suit and a lot of courage.
Yucca Mountain may also be inhabited by large mutated creatures, as in Mr. RADical's journal, the author mentions seeing "something big" moving down its tunnel.
Yucca Mountain is mentioned only in Fallout: New Vegas.