The Keystone Bridge was built around 1865 by the Keystone Bridge Comp-any, Pittsburg, Pennsylvania. The original location of the bridge is unknown. The Colorado Southern Pacific Railroad acquired the bridge sometime prior to 1903. The bridge was erected at Mill Gulch across the South Platte River, a few miles south of Denver, near Waterton.
In 1978, when construction began on the Strontia Springs Dam, the Denver Water Board dismantled the bridge.
On 1985 the Army Corps of Engineers re-assembled the bridge at it present location. The Keystone Bridge Company's unique wrought iron construction may be seen in the bridge. It consists of columns of 4 sections, held together with threaded bolts. The bridge is a rare example in the west and the only known bridge in Colorado created by the Keystone Bridge Company.