The original east-west main line of the Denver & Rio Grande, constructed in the 1870s and 1880s, was built as a narrow-gauge railroad, with the rails spaced three feet apart. The line ran from Denver south to Pueblo, and then turned west through the Royal Gorge to Salida. The route then continued over Marshall Pass to Gunnison, Montrose, and Grand Junction, before entering Utah and proceeding to Salt Lake City and Ogden. This existed as a through route only until 1890, when the main line was standard-gauged. The standard gauge route headed north from Salida via Tennessee Pass, rejoining the original narrow-gauge route at Grand Junction. This left the old narrow-gauge line over Marshall Pass as a local route. Narrow-gauge trains operated between Salida and Grand Junction until the Montrose-Grand Junction tracks were standard-gauged in 1906, truncating the narrow-gauge line to a Salida-Montrose route.