Geology
The rock layer enclosing the fossils is a sandstone and conglomerate bed of alluvial or river bed origin known as the Morrison Formation from the Jurassic Period some 150 million years old. The dinosaurs and other ancient animals were washed into the area and buried presumably during flooding events.
The pile of sediments were later buried and lithified into solid rock. The layers of rock were later uplifted and tilted to their present angle by the mountain building forces that formed the Uintas. The relentless forces of erosion exposed the layers at the surface to be found by paleontologists.
Read more about this topic: Dinosaur National Monument