The east-dipping Mesozoic formations of the Defiance monocline in the Chuska Mountains along the Arizona-New Mexico state line are overlain unconformably by flat Tertiary sediments which have a maximum preserved thickness of almost 2,000 feet (Fig. 1). At the southern end of the mountains, above Tohatchi, New Mexico, the lower part of the Tertiary sediments was named by Gregory (1917) the Tohatchi shale. Allen (1953) in a recent note in this Bulletin has redefined the Tohatchi shale, assigning it as a conformable formation in the Mesaverde group (Upper Cretaceous), which is below the unconformity. Discussion of the note...

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