Yucca Mountain, at some point, became a nuclear waste repository where spent fuel rods and high level nuclear waste was dumped. After the Great War, Yucca became abandoned by humans and highly radioactive because of its contents left unchecked. No prospector dares to enter Yucca without a good radiation suit.
Yucca Mountain may also be inhabited by mutated creatures as in Mr. RADical's journal, he mentions seeing "something big" moving down it's tunnel.
Yucca Mountain is mentioned in Fallout: New Vegas.