Throughout its existence, the Rio Grande had over 10,000 narrow gauge freight cars of various types. Its roster peaked at about 6,000 freight cars in 1883, a time when its narrow gauge system was at its full extent (over 1,600 miles long). Then the number of freight cars slowly declined as lines were converted to standard gauge and narrow gauge lines were progressively abandoned. In 1968, when the freight operations ended on the narrow gauge, the Denver & Rio Grande Western still owned almost 1,000 narrow gauge freight cars, most of them being ancient models, mainly made of wood and many times rebuilt. The first narrow gauge freight cars built for the Denver & Rio Grande in 1871 were small 4-wheel cars, partially derived from the rolling stock of the Festiniog Railway, a 2ft gauge railroad in Wales. Too light and having a too small capacity, these early cars were rapidly replaced by several types of larger cars equipped with trucks. The specifications of these 8-wheel cars then evolved with time to meet the needs of the railroad and comply with the safety regulations put in place by the Interstate Commerce Commission. A large part of the information contained in these pages about the Rio Grande freight car fleet comes from the excellent book of Robert E. Sloan, A century + ten of D&RGW narrow gauge freight cars, 1871 to 1981.