Archaeological evidence indicates that the tributary canyons and sheltered areas in the river valley were home to the Fremont Culture, which flourished from the 7th century to the 13th century.
The Fremont were a semi-nomadic people who lived in pithouses and are best known for the rock art on canyon walls and in sheltered overhangs.

In later centuries, the river basin was home to the Shoshone and Ute peoples, both nomadic hunters.
The Shoshone inhabited the river valley north of the Uinta Mountains, whereas the Utes lived to the south.
The current reservation of the Utes is in the Uintah Basin.
The Shoshone called the river the Seeds-kee-dee-Agie, meaning "Prairie Hen River."

In 1776, the Spanish friars Silvestre Vélez de Escalante and Francisco Atanasio Domínguez crossed the river near present-day Jensen, naming it the Rio de San Buenaventura.
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.
Later cartographers extended the error, representing the Buenaventura River as flowing into the Pacific Ocean.
At least one charted the Buenaventura as draining the Great Salt Lake.
Later Spanish and Mexican explorers adopted the name Rio Verde, meaning "Green River" in Spanish.
Exactly when the Spanish started using this name and why is unknown.
Explanations of the name "Green" include ideas about the color of the water (though it is usually just as red as that of the Colorado), the color of soapstone along its banks, the color of the vegetation, and the name of a trapper.
No explanation can be verified.
Wilson Hunt of John Jacob Astor's Pacific Fur Company called it The Spanish River in 1811.
By that time it was clear to the trappers that Miera's map (if they had seen it) was wrong, for they had learned from the Native Americans that the Green River drained to the Colorado River and the Gulf of California.
When Jedediah Smith reached the lower Colorado in 1826 he at first called it the Seedskeedee, as the Green/Colorado River was commonly known among the trappers.
By the time of Bonneville's expedition in 1832, the names "Seeds-kee-dee", "Spanish River", "Green River", and even "Colorado River" were used interchangeably by the trappers and American explorers.

While it was known that the Green River drained to the Colorado, the exact course was not known.
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 the Colorado per information from the Native Americans).
A map of 1847 redirects the course of the Rafael to the north and labels it as Green River.
It would be some time before the true confluence of the Green and Colorado Rivers would be known.

The Old Spanish Trail from New Mexico to California crossed the river just above the present-day town of Green River, Utah.

In the early 19th century, the upper river in Wyoming was part of the disputed Oregon Country.
It was explored by trappers from the North West Company and Hudson's Bay Company, such as Donald Mackenzie who pioneered the area, from 1819.
In 1825, the American William Ashley and a party of American explorers floated down the river from north of the Uintah Mountains to the mouth of the White River.
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.
The Upper Green River Rendezvous Site near Pinedale, Wyoming was a popular location for annual mountain man rendezvous during the 1820s and 1830s, with as many as 450 to 500 trappers attending during its heyday in the 1830s.

The region was explored by John C. Fremont on several of his expeditions in the 1840s.
Fremont corrected the cartographic error of Miera, establishing firmly that the river did not drain the Great Salt Lake.
In 1869, the river was
Archaeological evidence indicates that the tributary canyons and sheltered areas in the river valley were home to the Fremont Culture, which flourished from the 7th century to the 13th century. The Fremont were a semi-nomadic people who lived in pithouses and are best known for the rock art on canyon walls and in sheltered overhangs.
In later centuries, the river basin was home to the Shoshone and Ute peoples, both nomadic hunters. The Shoshone inhabited the river valley north of the Uinta Mountains, whereas the Utes lived to the south. The current reservation of the Utes is in the Uintah Basin. The Shoshone called the river the Seeds-kee-dee-Agie, meaning "Prairie Hen River."
In 1776, the Spanish friars Silvestre Vélez de Escalante and Francisco Atanasio Domínguez crossed the river near present-day Jensen, naming it the Rio de San Buenaventura. 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. Later cartographers extended the error, representing the Buenaventura River as flowing into the Pacific Ocean. At least one charted the Buenaventura as draining the Great Salt Lake. Later Spanish and Mexican explorers adopted the name Rio Verde, meaning "Green River" in Spanish. Exactly when the Spanish started using this name and why is unknown. Explanations of the name "Green" include ideas about the color of the water (though it is usually just as red as that of the Colorado), the color of soapstone along its banks, the color of the vegetation, and the name of a trapper. No explanation can be verified. Wilson Hunt of John Jacob Astor's Pacific Fur Company called it The Spanish River in 1811. By that time it was clear to the trappers that Miera's map (if they had seen it) was wrong, for they had learned from the Native Americans that the Green River drained to the Colorado River and the Gulf of California. When Jedediah Smith reached the lower Colorado in 1826 he at first called it the Seedskeedee, as the Green/Colorado River was commonly known among the trappers. By the time of Bonneville's expedition in 1832, the names "Seeds-kee-dee", "Spanish River", "Green River", and even "Colorado River" were used interchangeably by the trappers and American explorers.
While it was known that the Green River drained to the Colorado, the exact course was not known. 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 the Colorado per information from the Native Americans). A map of 1847 redirects the course of the Rafael to the north and labels it as Green River. It would be some time before the true confluence of the Green and Colorado Rivers would be known.
The Old Spanish Trail from New Mexico to California crossed the river just above the present-day town of Green River, Utah.
In the early 19th century, the upper river in Wyoming was part of the disputed Oregon Country. It was explored by trappers from the North West Company and Hudson's Bay Company, such as Donald Mackenzie who pioneered the area, from 1819. In 1825, the American William Ashley and a party of American explorers floated down the river from north of the Uintah Mountains to the mouth of the White River. 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. The Upper Green River Rendezvous Site near Pinedale, Wyoming was a popular location for annual mountain man rendezvous during the 1820s and 1830s, with as many as 450 to 500 trappers attending during its heyday in the 1830s.
The region was explored by John C. Fremont on several of his expeditions in the 1840s. Fremont corrected the cartographic error of Miera, establishing firmly that the river did not drain the Great Salt Lake. In 1869, the river was 
Green River (Colorado River tributary)