MESA VERDE NATIONAL PARK, Colo. (AP) -- Archeologists at Mesa Verde National Park say a crack is threatening the southern half of the park's largest and most famous cliff dwelling.

The park announced Friday that the crack and other related structural problems is the reason why visitors have been kept away from the edge of a kiva on tours of Cliff Palace this summer. Wooden braces are now shoring up the kiva, a round, Pueblo Indian ceremonial structure built in the 13th century.

The crack was discovered last summer but it's not the only problem archeologists are working to fix. Cliff Palace was built on a sloping alcove floor and, over time, it has been sliding downslope. Dripping water has been a long-standing problem, too, but water is now being rerouted away from the building.