Tourists climb wooden stairs to reach Balcony House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Cliff Palace, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Cliff Palace, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
(credit: CBS)
Mesa Verde National Park
Tourists look at the ruins of Spruce Tree House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
(credit: CBS)
Mesa Verde National Park
A view of a kiva at Spruce Tree House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
Rain falls over burnt trees in a burn area at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
(credit: CBS)
Mesa Verde National Park
A view of Spruce Tree House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
(credit: CBS)
Mesa Verde National Park
A view of one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
(credit: CBS)
Mesa Verde National Park
A view of Spruce Tree House, one of the cliff dwellings built the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Spruce Tree House, one of the cliff dwellings built the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Spruce Tree House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Square Tower House, one of the cliff dwellings built by Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Balcony House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Cliff Palace, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Balcony House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Spruce Tree House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of Balcony House, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Square Tower House, one of the cliff dwellings built by Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of the Cliff Palace, one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)
Mesa Verde National Park
A view of one of the cliff dwellings built by the Ancestral Puebloans at Mesa Verde National Park, taken on May 14, 2015. (credit: MLADEN ANTONOV/AFP/Getty Images)