On his way to explore the undiscovered region of Yellowstone in 1871, the American painter Thomas Moran hopped off his train early near Green River, Wyo. There he found an active railroad town nestled at the base of beautiful but imposing cliffs striated with stunning bands of color.

When he painted the scene, however, he substituted Indian travelers for the town and the railroad, depicting a scene that none could have seen in 1871. He conjured instead the dramatic, untamed wilderness that his Eastern patrons imagined the unfamiliar West to be.
Erasing civilization had its merits.

Moran’s Green River paintings are now considered his best, although he earned his eventual fame for his paintings of Yellowstone. Most celebrated among the Green River series is “Green River Cliffs, Wyoming,” which the National Gallery of Art recently acquired.

Painted in 1881, it is the gallery’s third painting by the 19th-century artist and a gift of longtime Western art collector Vern Milligan and his two children. Milligan purchased “Green River” at auction in 1994 for $2.7 million. He has since kept it in his private collection, according to the gallery.

“It was one of the stars of the [1997] show,” said Nancy Anderson, curator of the gallery’s American and British paintings. “We admired the painting, and [Milligan] knew that and he decided this is where the painting belonged.”

“Green River” joins two other Moran paintings, including a central Pennsylvania landscape titled “The Juniata, Evening,” on display in the American galleries. A third Moran work, “The Much Resounding Sea,” which purportedly depicts a view of East Hampton, N.Y., is not on display.

“We have always lacked a grand panoramic view of the American West,” Earl A. Powell III, the National Gallery’s director, said in a press release. “‘Green River Cliffs, Wyoming’ fills this gap in spectacular fashion.”

With this arrival, the gallery can boast of representing all three of Moran’s most famous periods. “Green River” also joins two large depictions of Yellowstone and the Grand Canyon, Moran’s favorite Western vistas, at the Smithsonian American Art Museum. They are among his most famous works and particularly noteworthy because of the pivotal role that Moran’s watercolors played in Congress’ decision to declare Yellowstone the world’s first national park.

The painting will be on display outside the American galleries on the main floor of the museum’s West building through June 26.