Watch: Rock Fall Work Done At Mesa Verde's Cliff Palace

MESA VERDE NATIONAL PARK, Colo. (CBS4) - Workers at Mesa Verde recently had to bring down a large piece of sandstone that came loose over the Cliff Palace dwelling.

"All of these sandstone alcoves are unstable, and small pieces often fall," Mesa Verde posted on their Facebook page. "When bigger rocks threaten, we try to knock them loose."

The work at the Cliff Palace was done in August, but the video not posted to their page until Tuesday.

"Sometimes, the threatening rocks are so large that we have to close down whole alcoves," the park posted.

The Spruce Tree House, which is a large dwelling located near the Chapin Mesa Archaeological Museum, has been closed to tours for the last year due to that rock fall danger.

The Cliff Palace is located a short drive from the Spruce Tree House on the southeast side of Mesa Verde National Park.

It is the largest dwelling in the park, with approximately 150 rooms that is believed to have housed a population of 100 people.

The dwellings have reopened for Ranger-led tours, but tickets are required. They can be purchased at the park's visitor and research center, which is located near the entrance.