US 6 continues alone through the Spanish Fork Canyon, now alongside Soldier Creek, to Soldier Summit on the Wasatch Plateau, where it finally leaves the Great Basin into the watershed of the Colorado River. It begins to descend by following the White River, which empties into the Price River near Colton. The Price River takes US 6 down through the Price Canyon, the west edge of the Book Cliffs, joining US 191 at Castle Gate. The land flattens and opens out at Helper, named for the helper locomotives needed to carry trains up to Soldier Summit, and US 6 continues southeasterly around Price on a two-lane freeway bypass, with the old alignment marked as both a business route and SR 55. Relatively flat land continues as US 6 parallels the Book Cliffs to the southwest and west, crossing the Price River at Woodside. West of Green River, US 6 joins I-70/US 50, which it overlaps for the remainder of its stay in Utah. Now south of the Book Cliffs, the four routes head east to Crescent Junction, where US 191 splits to the south. As it begins to approach the Colorado River, the highway curves northeasterly through the Grand Valley and into Colorado.