Dale Creek Crossing (Wyoming) on the Union Pacific Railroad ca. 1870.

From wikipedia: The 650 feet Dale Creek Crossing, completed in 1868 in southeastern Wyoming Territory presented engineers of the United States’ first transcontinental railroad one of their most difficult challenges. Dale Creek Bridge, the longest bridge on the Union Pacific Railroad, reached 125 feet above Dale Creek, two miles west of Sherman, Wyoming. The eastern approach to the bridge site, near the highest point on the Union Pacific Railroad, 8,247 feet required cutting through granite for nearly a mile. Solid rock also confronted workers on the west side of the bridge where they made a cut one mile long.

Originally built of wood, the trestle swayed in the wind as the first train crossed on April 23, 1868. In the days following, as carpenters rushed to shore up the bridge, two fell to their deaths. Still, the bridge’s timbers flexed under the strain of passing trains.

(Museum of Photographic Arts/Tehrkot Media)