Among those sites identified as Chacoan outliers, the Chimney Rock Pueblo is distinguished by being the most isolated, the highest, and the most remote from arable land. With two exceptions, building at all of the outliers was begun between A.D. 1086 and the first half of A.D. 1120. Chimney Rock Pueblo is one of those exceptions, as construction began in A.D. 1076. — from Prehistoric Astronomy in the Southwest, by J. McKim Malville and Claudia Putnam
[mjh: notice that's 10 years before others; anyone know what the other exception is?]
Chimney Rock is located in southwestern Colorado. It is one of the northernmost Chacoan outliers (Lowry Ruin is farther north and west). It's clear that the main reason for building in this area are two natural stone pillars, Chimney Rock and Companion Rock. Looking from various vantage points from the west to the east, both the sun and moon rise between these two pillars in a very predictable manner (predictable to shrewd observers like the Anasazi). This picture (from a US Forest Service postcard) shows the great house in the lower right, Chimney Rock in the upper left, and the mountains near Pagosa Springs in the background).
Construction of the great house as well as villages on nearby ridges clearly was planned to highlight (and anticipate) major solar and lunar events, including equinoxes, solstices and so-called "lunar standstills" (part of an 18.6 year lunar cycle).
Below is Companion Rock and Chimney Rock and the gap between them through which many astronomical observations would have been made. This is the view just beyond the upper Great House (from the fire watchtower). Put your mouse over the image for a close-up.