Aztec was inhabited for about 200 years, with the first arrivals coming about 1088-1090, and the deepest excavations have found Chacoan pottery. According to tree-ring dating the West Ruin was built between 1111 and 1115 AD. This 450-room pueblo includes one of the few tri-wall kivas ever found. By the 13th century this pueblo may have equaled Chaco in size.

A severe drought began in 1130 that was to last 60 years, and by 1150 the Chacoan social and economic center was declining which impacted Aztec as well as Salmon Ruin. Though the region was mostly abandoned, some local peoples of the San Juan Valley lived at both sites until about 1185 and they used the structures as they found them.

Then people related to the Mesa Verdans took over in 1225, and changes in the architecture were made, consisting mainly of dividing the large rooms and building many small kivas within the large square and rectangular rooms.

As each succeeding group moved in they depleted the resources of the area according to their preferences and moved on. A drought from 1276 to 1299 was the telling blow and the last inhabitants left in the 1300's.

The first person we know of to visit Aztec Ruins was a geologist, Dr. John S. Newberry, in 1859. At that time the site was undisturbed.

By 1878, when anthropoligist Lewis H. Morgan came to the ruins, about one-fourth of the stones had been used as building materials by settlers. Looting continued until 1889, when the site became privately owned.

Then in 1916 excavating was sponsored by the American Museum of Natural History; Aztec Ruins was made a national monument in 1923, and became a World Heritage Site in 1987.

The Great Kiva was reconstructed by Earl Morris in the 1930's and is the largest fully reconstructed kiva in North America.

Aztec Ruins is 320 acres in size and is administered by the National Park Service, Department of Interior.