<P> The Cliff House Sandstone is the area's youngest rock layer . It was formed after the Cretaceous sea had completely receded and as a result has a high sand content from beaches, dunes, etc. and from this receives its characteristic yellow tint to its canyon faces . Like the Point Lookout Sandstone, it is about 400 feet thick . It contains numerous fossil beds of different types of shells, fish teeth, and other invertebrate leftovers from the receded sea . The shale zones in this feature determine where alcoves formed where the Ancestral Puebloans constructed their dwellings . </P> <P> Continuing through the Cretaceous period and into the early Tertiary, there was uplifting in the area of the Colorado Plateau, the San Juan Mountains, and the La Plata Mountains, which led to the formation of the Mesa Verde pediment with the help of erosion . Small channels of water ran across this formation depositing gravel . Later in the tertiary, the last period of uplift and rock tilting towards the south caused these streams to cut rapidly into the rock removing loose sediment and forming the vast canyons seen today . This caused the isolation of the Mesa Verde pediment from surrounding rock . Today, since the climate is more arid, these erosional processes are slowed . </P> <P> Mexican - Spanish missionaries and explorers Francisco Atanasio Domínguez and Silvestre Vélez de Escalante, seeking a route from Santa Fe to California, faithfully recorded their travels in 1776 . They reached Mesa Verde (green plateau) region, which they named after its high, tree - covered plateaus, but they never got close enough, or into the needed angle, to see the ancient stone villages . They were the first white men to travel the route through much of the Colorado Plateau into Utah and back through Arizona to New Mexico . </P> <P> The Mesa Verde region has long been occupied by the Utes, and an 1868 treaty between them and the United States government recognized Ute ownership of all Colorado land west of the Continental Divide . After there had become an interest in land in western Colorado, a new treaty in 1873 left the Ute with a strip of land in southwestern Colorado between the border with New Mexico and 15 miles north . Most of Mesa Verde lies within this strip of land . The Ute wintered in the warm, deep canyons and found sanctuary there and the high plateaus of Mesa Verde . Believing the cliff dwellings to be sacred ancestral sites, they did not live in the ancient dwellings . </P>

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