A Geologic History of Cache Valley

The oldest rocks in Cache Valley are probably the ledges and cliffs on the mountains. The limestone cliffs, like Logan Canyon's China Wall, are ancient limestone. Some 500 million years ago, the rock record shows us that Cache Valley was actually the bottom of the Pacific ocean.

The fossil corals, trilobites, and other fossils found in the limestone indicate that the ocean that covered Cache Valley was probably a warm, tropical sea.

The scenery at Tony Grove, at an altitude of 8,000 feet shows the ocean plainly. The brownish-pink rocks near the lake are the ancient sea-bed and beach. The grey rocks above are limestone formed by millenia (thousands of years) of shells and skeletons that "rained" down on the ocean bottom. Most of the intact fossils are found in the grey limestone.

About 250 million years ago as the land began to rise, probably as a great plain, the ocean was forced westward across Idaho and Nevada.

The rock record in Cache Valley is missing a very important period of the earth's history.

Fossils are usually found jumbled as shown in the top-center picture. Cache Valley seems to have no dinosaur fossils. Such fossils are abundant 150 miles to the east. Perhaps the fossil bearing rocks slid to the east when the Rocky Mountains rose, or they may lay buried deep beneath the Valley floor or perhaps rocks from that era simply eroded away.


The paleontologist's dream is to find an articulated skeleton (the bones are connected in a skeleton) like the Stegosaurus at the center bottom. As a boy growing up in Providence, I remember sitting in the school library and reading Roy Chapman Andrews' books about his expedition's dinosaur fossil finds in the Gobi desert. We may never find dinosaur fossils in Cache Valley, but our rocks tell other stories if we are just willing to observe and understand.