(There are three hotspots on this image which lead to close-ups of the various parts of the ruin.)
The age of these ruins is undetermined, but it is thought that by about 1300 AD all the Puebloan people who built these dwellings had departed the area, heading south to rejoin other related tribes, the Zuni, the Acoma, and the Hopi, in the area near present-day Albuquerque. When the Navajo and Apache migrated into this area shortly afterward, they found abandoned structures probably not much changed from what we can see today.
The Navajo word for these people is 'Anasazi', a word which means 'ancient enemy'. Naturally, the modern Puebloans prefer this term to be retired permanently.