U.S. Route 91 (US 91) is a north–south United States highway. The highway currently serves as a connection between the Cache Valley area of Utah and Idaho to the Salt Lake City and Idaho Falls population centers. Prior the mid-1970s, US 91 was an international commerce route from Long Beach, California to the Canadian border north of Sweetgrass, Montana. US 91 was routed on the main street of most of the communities it served, including Las Vegas Boulevard in Las Vegas and State Street in Salt Lake City. From Los Angeles to Salt Lake, the route was built along the corridor of the Arrowhead Trail. US 91 has been largely replaced by Interstate 15. A portion of the highway's former route in California is currently State Route 91.