DENVER (AP) – A handful of sites where the United States manufactured and tested some of the most lethal weapons known to humankind are now havens for wildlife.

Six obsolete weapons complexes – mostly for nuclear or chemical arms – are home to an astonishing array of animals and habitats because the sites banned the public and other intrusions for decades.

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(credit: CBS)

They’re now refuges managed by the U.S. Fish and Wildlife Service.

The cost of the conversions is staggering. An Associated Press review shows the government and private companies have spent more than $57 billion so far, and it could take more than $323 billion to finish.

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Critics say the sites haven’t been cleaned well enough to make them safe for humans. They say significant contamination was left behind, and the government will have to monitor it for centuries.

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