The Morrison Formation is an upper Jurassic sedimentary rock unit best known in the Western States of Colorado, Utah and Wyoming. In Wyoming, it ranges into the Bighorn basin where the Dana Quarry is located. Throughout most of its range, the Morrison Formation comprises mudstone, sandstone, siltstone and limestone and its layers are light grey, greenish gray, or red. However, at the Dana Quarry site the soft sand layers containing fossils are predominately yellow-brown in color. These yellow layers preserve both plant and animal remains in abundance possibly marking a unique depositional event.
In the late 1800s, the Morrison Formation was essentially the center of the Bone Wars, a fossil collecting rivalry between paleontologists Othniel Charles Marsh and Edward Drinker Cope. This formation is one of the most productive geological layers in the history of paleontology, and a unique treasure of the American West. The popular dinosaurs, Apatosaurus, Stegosaurus, and Allosaurus were all first discovered in the Morrison. Radiometric tests place the age between 148 and 155 million years (i.e., the Oxfordian, Kimmeridgian, and earliest Tithonian stages of the late Jurassic). It is thus similar in age to the Solnhofen Limestone of Germany.
The Dana Quarry appears to be situated within the lower part of the Morrison Formation. The fossil producing layers are approximately 20 feet above the Sundance Formation, where the contact of these two formations is visible on the eastern slope of the site. On the ranch property, looking west from the Quarry one can see conglomerate sandstone possible remnants of the Cloverly Formation sitting on the Morrison. Thus, the Morrison Formation here appears to be sandwiched between the Cloverly above and the Sundance below. Unless there exists unconformity between the two formations, the Dana Quarry can be considered Lower Morrison in age. This age determination may be significant, as localities producing older faunas are quite rare in the Morrison.