Keet Seel is a Navajo term meaning "Broken pottery scattered around."
The people started building the cliff dwelling around 1250 CE but between 1272 and 1275 there was a sudden building spurt. Then construction slowed until it stopped completely in 1286. Within 20 years the pueblo was completely abandoned. The Navajo stumbled over the site more than 300 years later.
The ruins of Keet Seel were so well protected by the canyon wall it was built into that the pueblo is among the best preserved of all ancient constructions in North America. At its height, there were more than 150 rooms built, including some that were just for storing grain. There were also six kivas.
Apparently, the local environment was good enough to support a relatively large population and provide them with food surpluses. That said, the peak population of around 150 people may have also contributed to the abandonment as the climate continued to get more dry up to about 1300 CE (not that they would have known anything about that arbitrary number).
In the ruins of Keet Seel a dessicated parrot body was found, with a few feathers still attached. That bird had to have been brought north by traders from Mesoamerica almost 800 years ago.
Keet Seel is located within the archaeological area known as "Kayenta-Tusayan." Today it is part of "Navajo National Monument." Interesting as none of the three non-contiguous pieces of that Monument have anything to do with the Navajo people. They were all abandoned long before the Navajos arrived in the area. And another note: the Navajo had left the ruins alone and removed nothing during the centuries that they knew about them. The first Euro-Americans to find the ruins began looting artifacts and selling them almost immediately.
Archaeologists have proposed reasons for the abandonment based on changes in weather patterns. The Hopis tell a story more of a spiritual quest concerning the Snake and the Horn clans. In the Hopi story, the Horn clan forced the Snake clan out because the Snake clan children were biting other children and causing them to die. The story is likely an allegory for an actual historical event: as the climate got more dry, rattlesnakes probably became more of a problem. In this case, members of the Snake clan are recorded to have relocated directly to the village that was Walpi at the time: at the foot of 1st Mesa.
The Horn clan is recorded to have relocated to a Flute clan pueblo northeast of Walpi named Leñanobi. There might have been a couple generations passing at Leñanobi before that pueblo was abandoned and the Flute and Horn clans moved to Walpi, too.