The late Cenozoic geology of the Colorado Plateau is relatively unknown compared to that of the earlier epochs and periods. This condition exists despite the great interest in the late geologic history of the Plateau and the Colorado River, an interest that has continued unabated since the days of the early, explorations. It is not for lack of work in the region that this condition exists, for much has been accomplished and written about it. The cause lies in the facts that the region is vast, that most of the record has been destroyed by erosion, and that the problem thereby is very difficult. When the Cenozoic geology and history of the Plateau are finally unravelled it will probably not be as the result of brilliant perception and deduction, but rather as the result of persistent and careful study of the scattered bits of remaining .evidence. The challenge of this unsolved problem, however, cannot be easily ignored by one working in the area, and it finally led the writer to undertake a comprehensive study of the late Cenozoic geology of a portion of the Plateau. It is hoped that this study, though it has not deciphered the Plateau's history, has at least produced some much needed basic data concerning it. The Chetoh country,of Arizona and New Mexico was chosen for the study because as far as the writer knows, it contains the most complete record of the late Cenozoic geology of the Plateau.