The Green River rises in western Wyoming, in northern Sublette County, on the western side of the Continental Divide in the Bridger–Teton National Forest in the Wind River Range.
It flows south through Sublette County and western Wyoming in an area known as the Upper Green River Valley, then southwest and is joined by the Big Sandy River in western Sweetwater County.
At the town of La Barge, it flows into Fontenelle Reservoir, formed by Fontenelle Dam.
Below there, it flows through open sage covered rolling prairie where it is crossed by the Oregon, California and Mormon emigration trails  and then further south until it flows past the town of Green River and into the Flaming Gorge Reservoir in Southwestern Wyoming, formed by the Flaming Gorge Dam in northeastern Utah.
Prior to the creation of the reservoir, the Blacks Fork joined the Green River south of Green River, today the mouth of Blacks Fork is submerged by the reservoir.

South of the dam it flows eastward, looping around the eastern tip of the Uinta Mountains going from Utah into northwestern Colorado and through Browns Park before turning west and then south into Dinosaur National Monument where it passes through the Canyon of the Lodore (Otherwise known as the Gates of Lodore) and is joined by the Yampa River at Steamboat Rock.
It turns westward back into Utah along the southern edge of the Uintas in Whirlpool Canyon.
In Utah it meanders southwest across the Yampa Plateau and through the Uintah and Ouray Indian Reservation and the Ouray National Wildlife Refuge.
Two miles south of Ouray, Utah, it is joined by Duchesne River, and three miles (5 km) downstream by the White River.
Ten miles farther downstream it is joined by the Willow River.

South of the plateau, it is joined by Nine Mile Creek, then enters the Roan Cliffs where it flows south through the back-to-back Desolation and Gray canyons, with a combined length of 120 mi (192 km).
In Gray Canyon, it is joined by the Price River.
South of the canyon it passes the town of Green River, Utah and is joined by the San Rafael River in southern Emery County.
In eastern Wayne County it meanders through Canyonlands National Park where it joins the Colorado.

The Flaming Gorge Dam in Utah is a significant regional source of water for irrigation and mining, as well as for hydroelectric power.
Begun in the 1950s and finished in 1963, it was highly controversial and opposed by conservationists.
 Originally, a dam was to be built in Whirlpool Canyon, but the conservationist movement traded the Flaming Gorge dam for halting that proposal.
Apocryphally, the Sierra Club, a not-for-profit environmental organization, lost its tax-exempt status for political action in opposing the proposed dam.

The Green is a large, deep, powerful river.
It ranges from 100 to 300 feet (30 to 100 m) wide in the upper course to 300 to 1,500 feet (460 m) wide in its lower course and ranges from 3 to 50 feet (1 to 15 m) in depth.
It is navigable by small craft throughout its course and by large motorboats upstream to Flaming Gorge Dam.
Near the areas where the Oregon Trail crosses, the river is 400 - 500 feet (150 m) wide and averages about 20 feet (6.1 m) deep at normal flow.
The Green River rises in western Wyoming, in northern Sublette County, on the western side of the Continental Divide in the Bridger–Teton National Forest in the Wind River Range. It flows south through Sublette County and western Wyoming in an area known as the Upper Green River Valley, then southwest and is joined by the Big Sandy River in western Sweetwater County. At the town of La Barge, it flows into Fontenelle Reservoir, formed by Fontenelle Dam. Below there, it flows through open sage covered rolling prairie where it is crossed by the Oregon, California and Mormon emigration trails  and then further south until it flows past the town of Green River and into the Flaming Gorge Reservoir in Southwestern Wyoming, formed by the Flaming Gorge Dam in northeastern Utah. Prior to the creation of the reservoir, the Blacks Fork joined the Green River south of Green River, today the mouth of Blacks Fork is submerged by the reservoir.
South of the dam it flows eastward, looping around the eastern tip of the Uinta Mountains going from Utah into northwestern Colorado and through Browns Park before turning west and then south into Dinosaur National Monument where it passes through the Canyon of the Lodore (Otherwise known as the Gates of Lodore) and is joined by the Yampa River at Steamboat Rock. It turns westward back into Utah along the southern edge of the Uintas in Whirlpool Canyon. In Utah it meanders southwest across the Yampa Plateau and through the Uintah and Ouray Indian Reservation and the Ouray National Wildlife Refuge. Two miles south of Ouray, Utah, it is joined by Duchesne River, and three miles (5 km) downstream by the White River. Ten miles farther downstream it is joined by the Willow River.
South of the plateau, it is joined by Nine Mile Creek, then enters the Roan Cliffs where it flows south through the back-to-back Desolation and Gray canyons, with a combined length of 120 mi (192 km). In Gray Canyon, it is joined by the Price River. South of the canyon it passes the town of Green River, Utah and is joined by the San Rafael River in southern Emery County. In eastern Wayne County it meanders through Canyonlands National Park where it joins the Colorado.
The Flaming Gorge Dam in Utah is a significant regional source of water for irrigation and mining, as well as for hydroelectric power. Begun in the 1950s and finished in 1963, it was highly controversial and opposed by conservationists.  Originally, a dam was to be built in Whirlpool Canyon, but the conservationist movement traded the Flaming Gorge dam for halting that proposal. Apocryphally, the Sierra Club, a not-for-profit environmental organization, lost its tax-exempt status for political action in opposing the proposed dam.
The Green is a large, deep, powerful river. It ranges from 100 to 300 feet (30 to 100 m) wide in the upper course to 300 to 1,500 feet (460 m) wide in its lower course and ranges from 3 to 50 feet (1 to 15 m) in depth. It is navigable by small craft throughout its course and by large motorboats upstream to Flaming Gorge Dam. Near the areas where the Oregon Trail crosses, the river is 400 - 500 feet (150 m) wide and averages about 20 feet (6.1 m) deep at normal flow.
Green River (Colorado River tributary)