Chimney Rock Archaeological Area is located between Durango and Pagosa Springs, Colorado. Managed by the US Forest Service, tours are led by volunteers who are members of the Pagosa Chapter of the San Juan Mountains Association. The official website is www.chimneyrockco.org (brochure and lots of other info) and email is firstname.lastname@example.org. I'm told this volunteer support is something of a model for other Forest Service locations in the face of inadequate federal funding.
One cannot wander these ruins alone. Instead, tours are offered several times a day (between May 15 and September 30). Arriving for the first tour of the day, at 9:30am, I was lucky enough to have the guide to myself. Sarajane M. was informative & inspiring. Here she is standing under the oldest tree on the plateau (750 years or so).
During the period of its occupation, the Chimney Rock Pueblo may have been a pilgrimage and astronomical center that drew in visitors and communicated accurate calendrical information southward to Chaco Canyon. The meaning and fate of Chimney Rock appear to have been tied to Chaco and perhaps, Aztec, and Chimney Rock was abandoned sometime between A.D. 1130 - 1180, in unison with the dissolution of the Chaco regional system and its culture. Too isolated or too specialized in purpose, the Chimney Rock mesa was never reoccupied. — from The Astronomy of Chimney Rock, by J. McKim Malville.