The Rimrocks

The Rimrocks are geological rimrock sandstone formations that outcrop in sections of Billings, Montana.

Eighty million years ago the Billings metro area was the shore of the Western Interior Seaway, a sea that went from the present-day Gulf of Mexico to the Arctic North. Sediment and sand from the sea were deposited around the shoreline. Over time the sea rose and fell leaving behind a deep layer of sand. Over millions of years this sand was compressed into the sandstone the rims are made of. It is known as Eagle Sandstone.

Around a million years ago a much larger river than the current-day Yellowstone River began cutting a canyon into the valley floor of Eagle Sandstone, creating what today is known as the Rimrocks.