Wupatki is especially known for its pueblo ruins scattered all over the monument. The dwellings were established shortly after the eruption of the nearby Sunset Crater Volcano between 1040-1100. But over 200 million years ago, in the Lower Triassic, the geography of Wupatki was coastal floodplain as opposed to the desert it is now. Ancient reptiles in the genera Chirotherium and Rotodactylus trudged through the sand and mud that now form the rocks of the Moenkopi Formation that Wupatki National Monument sits on.