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The Ojo Alamo Sandstone of the San Juan Basin of New Mexico is composed of interbedded conglomeratic sandstone, sandstone, siltstone, and mudstone. Conglomerates are found in the western part of the basin; siliceous pebbles diminish in size both southward and eastward across the basin, becoming rare to nonexistent in the eastern part. There is great variation in the internal stratigraphy of the Ojo Alamo: Individual sandstone or mudstone beds thicken, thin, and pinch out laterally. The thickness of the Ojo Alamo varies from 6 m (20 ft) to more than 122 m (400 ft). The formation varies in composition from one to as many as five sandstone beds with interbeds of siltstone or mudstone.

Dinosaur bone has been found within the Ojo Alamo at several sites in the western part of the basin. Paleocene pollen has been found within the Ojo Alamo in the eastern part of the basin. To date, no Cretaceous pollen has been found at or above the stratigraphic level of dinosaur bone within the Ojo Alamo Sandstone. Near Barrel Spring, in the southwest part of the basin, both dinosaur bone and Paleocene pollen have been found. One bone, found at the top of the Ojo Alamo, was loose on the surface, and its significance is therefore equivocal. Dinosaur bone, however, has also been found in place in the upper part of the Ojo Alamo about 1.6 km (1 mi) west of Barrel Spring, at about the same stratigraphic level as Paleocene pollen from a site just east of Barrel Spring. Because there is no apparent unconformity between the highest in-place bone level and the Paleocene pollen level in this area, the Ojo Alamo dinosaurs, if not reworked, are Paleocene in age at this site and probably throughout the San Juan Basin.

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