US 91 followed the general path of the Arrowhead and Mormon Trails. It also was an important route connecting Southern California with the rest of the nation. US 91 was part of the original 1925 planning of the US numbered road system. Its western starting head was Long Beach, CA at the Long Beach Traffic Circle, where it was also met by the western end of US 6 and the eastern end was Sweetgrass, MT. When the California Route Renumbering occured, it was completely abolished inside the state. Its successor is Interstate 15 and all that remains of it is a 163 mile long stretch between Idaho Falls, ID and Brigham City, UT