The Lower Cretaceous conglomerate sandstone, sandstone, and mudstone interval stratigraphically between the Upper Cretaceous Dakota Sandstone and the Upper Jurassic Brushy Basin Member of the Morrison Formation in the Chama and northern San Juan basins, New Mexico and Colorado, is tentatively called the Burro Canyon(?) Formation. In this area the Burro Canyon(?) consists of a basal fluvial sequence deposited in braided-stream environments and an upper fluvial sequence deposited in braided to meandering-stream environments.

The Burro Canyon(?) is unconformably overlain by the Dakota Sandstone and may disconformably overlie the Brushy Basin Member of the Morrison Formation. The Burro Canyon(?) thins southward from the Chama and northern San Juan basins because of truncation of the formation under the

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pre-Dakota erosion surface.

The relation of the Burro Canyon(?) to the underlying Morrison Formation is less clear and has been the subject of controversy; the Burro Canyon(?) has at times been equated with the Jackpile-type sandstone at the top of the Brushy Basin Member in the San Ysidro area and along the east side of the San Juan basin. However, several lines of evidence, including facies relations, differing styles of sedimentation and sedimentary structures, and differences in composition of sandstone and mudstone of the upper part of the Brushy Basin Member and of the Burro Canyon(?) Formation in the San Juan and Chama basins, indicate that the Burro Canyon(?) Formation occurs stratigraphically above similar-appearing sandstones at the top of the Brushy Basin along the east side of the San Juan basin.

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