This image shows one of the two entrances to Royal Gorge by train, this one approaching from the east.
The description states:
THE ROYAL GORGE
The Royal gorge, the mother of the Arkansas River, is a gigantic slit or canal in the Rocky Mountains, cut from the summits of the lofty peaks to the very foundation stones. At the bottom flows the river and is built the D. & R. G. Railroad, an engineering feat looked upon as well-nigh impossible. A span wide in places and rising 3,000 feet perpendicular to the close, it presents miles of scenery equaled in few places on the globe. The swinging bridge is suspended from immense steel supports buried in the granite walls on either side.
–The D. & R. G. is the Denver and Rio Grande Railway, whose history in the building and operation of trains in the canyon is one of the more colorful and dramatic in the history of American railroading.
This postcard likely dates from the 1940s.