The Tri-Territory Site, a Sweetwater County historical monument


The Tri-Territory Site, 32 air miles northeast of Rock Springs. Photo courtesy of the Sweetwater County Historical Museum.

Wyo4News Staff, [email protected] [PRESS RELEASE]

December 30 – A remote, seldom-visited historical site in Sweetwater County, Wyoming, is the subject of a new article at – “The Tri-Territory Site: Outpost of Invisible Empires,” by Dick Blust of the Sweetwater County Historical Museum in Green River.

The site marks the spot along the Continental Divide near Steamboat Mountain where the borders of the Louisiana Purchase, the Mexican Cession, and the Oregon Country all met. By 1848, all three dominions had been incorporated into the United States and made up the overwhelming bulk of the American West outside of Texas.


In the 1960s, the Bureau of Land Management and the Kiwanis Clubs of Rock Springs, Riverton, Lander, and Rawlins launched the project that became the Tri-Territory Historic Site, a masonry monument and three flagpoles to represent Britain, Mexico, and France, with a fourth atop the monument itself for the United States. The site was formally dedicated on September 24, 1967.

To access “The Tri-Territory Site: Outpost of Invisible Empires,” go to, a project of the Wyoming Historical Society, is an excellent online resource for articles and information on Wyoming history.