Aztec Ruins National Monument is an large Ancestral Pueblo site near the Animas River in northwest New Mexico. It is misnamed, as is the town of Aztec, NM as the Aztecs of central Mexico had nothing to do with this area.
The West Ruins has been excavated and is a massive structure of about 400 rooms with three stories, with very thick walls. There is an equally large East Ruins that remains unexcavated and is not open to the public except on special tours. The trail that winds around the West Ruins is short, about 700 yards, but there is a lot to see.
It is thought that Aztec Ruins was originally occupied and influenced by the Chaco Canyon culture. Chaco Canyon is a major site about 55 miles to the south and was the main center of Pueblo culture until about 1100 AD. The center of Pueblo Culture shifted north to Mesa Verde after 1100 and Aztec Ruins shows these influences also. The inner walls here show the alternate sized bands of stones of the Chaco style and the outer walls show the more even sizes of Mesa Verde style.
There are a few places at Aztec where doorways are placed at corners, a rare feature and unique to the Chaco style. This was risky as it weakened the walls. One of the reasons that these structures eventually failed is that walls were not bonded well. Many of these walls were without solid foundations. As the walls settled, they tended to separate at the weak corners.
A structure just outside the main walls is called the Hubbard Tri-wall site. The space between the three concentric walls was divided into eight rooms in the inner circle and fourteen in the outer, with a central kiva. The site has been filled in with dirt to keep it from collapsing. Tri-wall sites are rare, but there is another one to see in Chaco Canyon at Pueblo del Arroyo site.
The environment at Aztec is dry and nearly desert, with only sparse Pinon Pine and Juniper trees growing. There was abundant water however from the Animas River, flowing down from the San Juan Mountains in southwest Colorado. This site was abandoned in the late 1200s as were all the Ancestral Pueblo sites in the Four Corners area.