Chaco Culture World Heritage Site

From about 850 Chaco Canyon was a major centre of the Ancestral Puebloans, and their society peaked between about 1020 and 1110. Pueblo Bonito began in the 10th century as a curved row of about 50 rooms and grew to at least 650 rooms, four storeys high in places. The canyon's buildings used the wood of about 200,000 conifers, much of it carried on foot from mountains up to 70 miles away.

Six road systems connected about 30 outlying communities to the canyon. The roads run up to 60 miles, are up to 30 feet wide and include stairways and ramps, but their purpose is uncertain. A 50-year drought began in 1130, and around 1140 the Chacoan system began to unravel.

In 1896 the Hyde Exploring Expedition of the American Museum of Natural History began excavating Pueblo Bonito and sent more than 60,000 artefacts to New York. The Antiquities Act of 1906 was passed partly in response to Richard Wetherill, who had worked for the expedition and in 1901 claimed a homestead that included Pueblo Bonito, and on 11 March 1907 President Theodore Roosevelt proclaimed Chaco Canyon a national monument. It became Chaco Culture National Historical Park on 19 December 1980 and was inscribed in 1987 together with Aztec Ruins, a national monument since 1923, and other sites.