Shortly after entering Utah, the Green enters Flaming Gorge, the first of a long series of canyons. Flaming Gorge, Horseshoe, and Kingfisher canyons are short but scenic. Red Canyon, the next in the series, is about thirty miles long, and is now the site of Flaming Gorge Dam. After Red Canyon, the Green enters Browns Park, a large east-west trending basin, and flows through it for fifteen miles before crossing the Colorado border.
The river flows through the northwest corner of Colorado for forty miles, through the Canyon of Lodore, and receives the waters of its largest tributary, the Yampa, while in Colorado. The Green re-enters Utah in the middle of Whirlpool Canyon, about five miles below its confluence with the Yampa. After passing through Island and Rainbow parks, the Green runs a short but turbulent seven miles through Split Mountain Canyon, which has the greatest fall of any of the canyons of the Green--almost twenty-one feet per mile--and consequently has some of the most difficult rapids on the entire river. Below the mouth of Split Mountain Canyon, the Green flows through the open, arid landscape of the Uinta Basin for more than 100 miles, unconfined by canyons and undisturbed by rapids. In the Uinta Basin two more large tributaries, the Duchesne River from the west and the White River from the east, join the Green, their mouths almost across from each other.