Late Triassic vertebrates from Revuelto Creek, Quay County, New Mexico
— Kenneth Carpenter and Michael Parrish

Fossil vertebrates from the Dockum Formation of eastern New Mexico have been known since the late 1800's, but the first major collection was made in 1916 by M. G. Mehl. Little additional collecting was made until the 1930's and late 1940's. During that time, material was collected for various universities and museums by E. C. Case, J. T. Gregory, J. W. Stovall, T. E. White and R. V. Witter (Gregory, 1972). These collections were important in correlating the vertebrate faunas of the Chinle Formation in Arizona with those of the Dockum Formation in northern Texas (e.g., Colbert and Gregory, 1957). Current work by Chatterjee (1983) is adding significantly to our understanding of the Dockum fauna of west Texas.

Some of the most important sites (Fig. 1) were discovered by Gregory along Revuelto Creek near San Jon in Quay County. Many of these sites were revisited in 1981 by the University of Colorado Museum in order to determine local stratigraphy and to locate any new fossils which may have eroded out since Gregory's work in the area. It was found that the most productive fossil horizon is a purple-weathering mudstone which caps the upper edge of the badlands along Revuelto Creek in secs. 10, 14, and 15, T9N, R33E. These mudstones overlie a thick sequence of unfossiliferous orange mudstone with large carbonate nodules scattered throughout. The purple mudstone contains lenses of crossstratified, reworked caliche as BB- and pea-sized carbonate nodules. 

One of these lenses was found to truncate a large phytosaur skull just in front of the orbits. The unweathered purple mudstone is grayishpink and criss-crossed by red streaks of iron stain. Numerous graymudstone interclasts are scattered throughout. Less fossiliferous horizons occur stratigraphically higher along Revuelto Creek as irregular channel sandstones. One exception is an exhumed channel composed of imbricated unionid shells.