The Rimrocks are geological rimrock sandstone formations in Billings, Montana. Eighty million years ago, the city's metro area was the Western Interior Seaway shore, a sea that went from the Gulf of Mexico to the Artic North. Sand and sediment from the sea were deposited around the shoreline. The Rimrocks (Rims) is an east-west route extending from the center to western Billings, MT above the city. There are many trails along with great vistas, biking, hiking and walking.