Billings is in the Yellowstone Valley which is a canyon carved out by the yellowstone river Around 80 million years ago, the Billings area was on the shore of the western interior seaway The sea deposited sediment and sand around the shoreline. As the sea retreated it left behind a deep layer of sand. Over millions of years this sand was compressed into stone that is known as eagle sandstone. Over the last million years the river has carved its way down through this stone to form the canyon walls that are known as the Billings rimrocks or the Rims
