The City of Roundup is located in the Musselshell Valley in east-central Montana, about 50 miles north of Billings. The Musselshell valley is drained by the Musselshell River, which flows from the Little Belt, Castle, and Crazy Mountains, through Roundup to Melstone where it turns abruptly north, passing through Mosby before flowing into Fort Peck Reservoir on the Missouri River. The Musselshell valley is bordered on the south by the Bull Mountains, which attain a maximum elevation of 4,700 feet. The name Musselshell is derived from the shells of freshwater mussels found in the river`s reefs. There is some conjecture as to whether the river was named by Lewis and Clark or derived its name from French or Indian names for the river. Lewis and Clark probably were the first white men to reach the Musselshell River, arriving at its mouth on the Missouri River May 4, 1805.