The transport of raw materials in bulk was the major source of traffic and revenue for the Denver & Rio Grande, and most of its lines were built to serve mines and to carry their products to ore processing plants. Among these raw materials, coal was by far the most important, but the railroad also carried iron ore and limestone from quarries. All these commodities were shipped in bulk using coal cars or gondolas. The Rio Grande owned over 3,000 gondolas of various types throughout its existence.
Until 1887, the classes of gondolas and of flat cars were not separate and the two types of cars were considered exchangeable by removing or adding sides to them. Between 1871 and 1887, the D&RG had 11 classes of gondolas built, according to plans and with parts from Billmeyer & Small, the first two classes were 4-wheel, the latter had trucks. Most of the cars from the oldest classes equipped with trucks (about 780 cars with a capacity of 8 to 10 tons in 1887) were removed from service at the turn of the 20th century, when the Interstate Commerce Commission imposed automatic couplers on freight cars. Some of these gondolas were dump cars, other were used as coke cars. The 15-ton and 20-ton gondolas built in the 1880s survived longer, some of them until the 1920’s and the last of them disappeared from the roster before 1950.
Between 1898 and 1906, the American Car & Foundry built 1,301 high side gondolas for the Rio Grande, 32ft long and with a capacity of 25 tons. They fell into 5 classes having slight differences in the height of their sides or the distance between their truck bolsters, and have been rebuilt in 1923 and 1926 by the D&RGW. They constituted the main body of the gondola fleet until the end of freight operations on the Rio Grande narrow gauge in 1968.
These gondolas were often quite different from one another even among cars of the same class, because of the frequent rebuildings and repairs due to damage caused by the rotary car dump used in Salida to mechanically unload them. High side gondolas #9200 to 9574 have been built between 1898 and 1902, 7 are conserved today on the Cumbres & Toltec Scenic Railroad, including #09410 now in the MOW fleet, and 2 other at the Colorado Railroad Museum. In 1902, #1000 to 1399 have been built, then #1400 to 1499 the same year, originally as side dump gondolas. Thirteen of these cars are preserved on the Cumbres & Toltec Scenic Railroad, including two converted to open observation cars, 3 other are at the Georgetown Loop Railroad, 4 on the Durango & Silverton Narrow Gauge Railroad and #1423 at the Colorado Railroad Museum. Numbers 1500 to 1899 have been built in 1903, 8 are now on the Cumbres & Toltec Scenic Railroad, one on the Durango & Silverton Narrow Gauge Railroad and another at the Georgetown Loop Railroad. Finally in 1906, the last high side gondolas were built (#1900 to 1925), they have all been scrapped in the early fifties.