MOUNT EVERTS, as viewed toward the northeast from the road south of Mammoth Hot Springs. The mountain, about 1,500 feet high above the plain, is formed by gently tilted sedimentary rocks of Cretaceous age, chiefly sandstone and shale of the Frontier, Cody, and Everts Formations ([fig. 5]). The conspicuous rimrock at the top of the mountain to the right is composed of the Yellowstone Tuff. When the tuff was deposited (by explosive eruptions from the south), there was no valley along the edge of the mountain. (Fig. 10)
FAUNAL SUCCESSION in sedimentary rocks. The different animals are now preserved as fossils, which are diagnostic of the period in which the animals lived. (Fig. 11)
| Man | ||
| CENOZOIC | QUATERNARY and TERTIARY | Mammals |
| CRETACEOUS | ||
| MESOZOIC | JURASSIC | Dinosaurs |
| TRIASSIC | ||
| PERMIAN | Reptiles | |
| PENNSYLVANIAN | Amphibians | |
| MISSISSIPPIAN | ||
| PALEOZOIC | DEVONIAN | Fishes |
| SILURIAN | Sea scorpions | |
| ORDOVICIAN | Nautiloids | |
| CAMBRIAN | Trilobytes | |
| PRE-CAMBRIAN | Soft-bodied creatures |
LIMESTONE OF MISSISSIPPIAN AGE along Pebble Creek at the Pebble Creek campground, northeastern Yellowstone National Park. (Fig. 12)
Closeup A shows one of the highly fossiliferous layers within the limestone.
Closeup B shows some of the fossils and their casts. Most of the fossils are of a variety of shelled sea animals (brachiopods) that lived on the ocean floors approximately 300 million years ago.