The Chesapeake & Ohio had ordered six dome cars for its ill-fated Chessie train, including three dome-sleepers and three dome observation cars. When the B&O purchased the dome-sleepers for its Capital Limited, the other three went to the Denver & Rio Grande Western. The Rio Grande apparently did not want observation cars (which require extra switching to turn them around at each end of a trip) and so it converted them for mid-train operation.
One of the Chessie dome-observation cars converted for mid-train use on the Royal Gorge. Note that the car next to it is a heavyweight car.
Starting in September, 1949, the Rio Grande added these cars to its Royal Gorge train, which connected Denver and Salt Lake City via Pueblo and Tennessee Pass–a longer route than the one followed by the California Zephyr. The Royal Gorge merged with the Prospector, which followed the same Denver-Salt Lake route as the Cal Zephyr on an overnight instead of a daytime schedule, in Grand Junction, so the Prospector too could say it was a dome-car train for at least part of its route. Since the Rio Grande had three of these domes, and only needed two for the Royal Gorge at any given time, it is likely that domes sometimes ventured east of Grand Junction on the Prospector trains.