CHACO CANYON, a tract of about 20,000 ac. in north western New Mexico, U.S.A., set apart in 1907 as a national monu ment. It contains the most remarkable architectural remains of prehistoric North America and has yielded a rich collection of objects illustrative of a vanished civilization. The buildings, which sometimes attained a height of at least four storeys, show a variety of methods in stone construction. Several are of enormous size, Pueblo Bonito, the largest, measuring 667 ft. by 315 ft.; a wall still standing rises to 48 feet. This building, like most of the others, constituted a veritable village and contained Boo rooms and 3 2 kivas, or large ceremonial halls. Chetro-Kettle and Penasco Blanco are similar structures, while other ruins show that the private house also was in use.