Nebraska, Colorado, Wyoming, Utah, Nevada, and California.

The route chosen by the Union Pacific Rail Road building west from Omaha was along the north side of the Platte River, and then through the Rockies at South Pass in Wyoming. Following the river took the railroad into Colorado Territory—but only for nine miles around Julesburg—and then back across the line into Nebraska again to follow Lodgepole Creek westward toward South Pass. Some 19th century maps of the railroad, compiled far away on the East Coast, weren't always punctilious about the exact relationship of the river, railroad, and state line, but the original line of road is still in use today by the Union Pacific, and easily seen on topographic maps or modern online map services.

Julesburg was one of the most raucous "Hell on Wheels" towns during the building of the railroad.

Text of a historical marker in Julesburg.

The Colorado Encyclopedia on the history of the various Julesburgs.