Much of the route traverses the arid Colorado Plateau, where the river has carved some of the most spectacular canyons in the United States.

The Green is slightly smaller than Colorado when the two rivers merge but typically carries a larger load of silt.

On July 25, 1921, the name change was made official in House Joint Resolution 460 of the 66th Congress, over the objections of representatives from Wyoming and Utah and the United States Geological Survey, which noted that the drainage basin of the Green River was more extensive than that of the Grand River,[4] although the Grand carried a higher volume of water at its confluence with the Green.

Below the dam, it flows through open sage-covered rolling prairie where it is crossed by the Oregon, California and Mormon emigration trails, and then further south past the town of Green River, Wyoming and into the Flaming Gorge Reservoir in southwestern Wyoming, formed by the Flaming Gorge Dam in northeastern Utah.

South of the dam, it is forced to turn sharply eastward by the uplift of the Uinta Mountains, looping around the eastern tip of the range as it travels 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.

[5] The Flaming Gorge Dam in Utah is a significant regional source of water for irrigation and mining, as well as for hydroelectric power.

The Fremont were semi-nomadic people who lived in pithouses and are best known for the rock art on canyon walls and in sheltered overhangs.

The map-maker of the expedition, Captain Bernardo Miera y Pacheco, erroneously indicated that the river flowed southwest to what is now known as Sevier Lake.

[6] Wilson Hunt of John Jacob Astor's Pacific Fur Company called it The Spanish River in 1811.

When Jedediah Smith reached the lower Colorado in 1826, he first called it the Seedskeedee, as the Green/Colorado River was commonly known among the trappers.

Miera's map showed the Colorado River branching into two major streams – the Nabajoo (San Juan) and the Zaguananas.

It also showed the Zaguananas branching into four heads, including the Dolores and the Rafael (the latter of which Escalante's journal equates with Colorado per information from the Native Americans).

The valley of the river became increasingly used as a wintering ground for American trappers in the next decades, with trading posts established at the mouth of the White near Whiterocks, Utah, and Browns Park.

Fremont corrected the cartographic error of Miera, establishing firmly that the river did not drain the Great Salt Lake.

In 1878 the first permanent settlement in the river valley was founded at Vernal by a party of Mormons led by Jeremiah Hatch.

The settlement survived a diphtheria epidemic its first winter, as well as a panic caused by the Meeker Massacre in Colorado.

A proposed nuclear power plant, the Blue Castle Project, is set to begin construction near Green River in 2023.

[13] The discovery of petroleum at the Ashley Field after World War II has led to the exploitation of oil and natural gas in the region.

[17] At the time of its discovery (2005), the Green River Formation was said to have the world's largest fossil fuel deposits in the form of a solid rock resource called[18] oil shale.

The mining operation is less expensive for the production of soda ash in the United States than the synthetic Solvay process, which predominates in the rest of the world.