I-15 continues through Utah for just over 400 miles (640 km). It is the main north-south connection for the state. The highway approximately follows the old alignment of U.S. Highway 91 from St. George to Brigham City. The highway passes through the fast-growing Dixie region, which includes St. George, Cedar City, and eventually most of the major cities and suburbs along the Wasatch Front, including Provo, Orem, Sandy, West Jordan, Salt Lake City, Layton, and Ogden. Around Cove Fort, Interstate 70 begins its journey eastward across the country. The interstate merges with I-80 for about 3 miles (5 km) from South Salt Lake to just west of Downtown Salt Lake City and also merges with Interstate 84 from Ogden to Tremonton. Along nearly its entire length through the state, I-15 winds its way along the western edge of a nearly continuous range of mountains (the Wasatch Range in the northern half of the state). The only exceptions are when it passes through the mountains south of Cedar City and again north of Cove Fort.