The Teton Range does not conjure visions of vast, ancient seas; the peaks seem too powerful and imposing. The landscape of Grand Teton National Park, however, reflects both scenes. Sedimentary rocks deposited by ancient seas drape over crystalline bedrock found in the high peaks. Fossils are the mineralized remains or impressions of plants or animals from the geologic past, and provide geologists with clues to unravel the history of the area.
Fossils occur in sedimentary rock. Material such as gravel, sand, or mud settles from water into horizontal layers. With time, these layers become buried, compressed, and lithify (harden to rock). Organic material such as plant and animal remains settles along with the sediment, buried within the layers. As the waters recede, sedimentary rocks are exposed to erosive forces such as wind, rain, ice and gravity. These forces break down the rocks exposing each successive underlying layer. Eventually, the fossil remains of a creature once buried under thousands of feet of sedimentary rock may be exposed at the Earth's surface.
Grand Teton National Park has exposures of sedimentary rocks over a thousand feet thick in the northern, southern, and, most dramatically, in the western portions of the park. Many of these formations contain the fossil remains of marine organisms. The presence of these fossils indicate that where the Teton Range now stands was once the floor of an ancient sea inhabited by algae, coral, brachiopods (clam-like shells), and trilobites.
Fossils do more than provide us with a fascinating look at prehistoric life forms. They are useful tools to date geologic features, analyze past climates and trace evolutionary processes. If you are fortunate enough to find a fossil during a visit to a national park, please look but do not take. Leave the fossils to be rediscovered by other visitors and scientists in the future.
Did You Know?
Did you know that lodgepole pine trees grow on glacial moraines in Jackson Hole? Glacial moraines are ridges of rocky debris left behind as Ice Age glaciers melted. The soil on these ridges retains moisture and is more hospitable to trees than the cobbly, porous soil on the outwash plain.