The Greeley, Salt Lake and Pacific Railway was a railroad that operated in northern Colorado in the United States during the 1880s.
The railroad received financial backing from the Union Pacific, which was concerned about plans by its rival, the Chicago, Burlington and Quincy Railroad, to extend its line westward from the South Platte River valley over the Rocky Mountains to Salt Lake City.
The GSLPRR constructed a line between Greeley and Fort Collins, as well as several spurs, one which went up into the foothills to the stone quarries at Stout at the present site of Horsetooth Reservoir.
The line skirted the Cache la Poudre River in Fort Collins, along the current Willow Street.
Although the Union Pacific sponsored surveying expeditions up the Poudre Canyon, with the intention of possibly extending the line over Cameron Pass into North Park, the parent railroad lost interest in the project after the abandonment of the similar plans by its rival, the Chicago, Burlington and Quincy.