Rail transportation reached the San Luis Valley when the narrow gauge Denver & Rio Grande Railway was completed to Alamosa in 1878, and the track was standard-gauged in 1899. Efforts to cultivate the valley showed both fertile soil and the need for irrigation, and a review of precipitation data for 1895-1905 suggested that the west slope of the Sangre de Cristo range could be profitably developed for agriculture with irrigation. Eastern capitalists then organized the Costilla Estates Development Company, which installed reservoirs, ditches, and townsites, and separately organized the San Luis Southern Railway to build from Blanca to Taos, NM. In 1910 the line completed 29 miles of track south to Jaroso, CO, but the Costilla Estates project had relied on overly optimistic precipitation estimates, so harvests and land sales fell short of expectations and the railway never advanced beyond Jaroso, ending 300 feet short of the New Mexico boundary. In January 1928 its assets were sold at foreclosure and became the San Luis Valley Southern Railway. Although improved agricultural harvests helped the new line, rising highway competition hurt carloadings, and efforts to extend southward as the advertised "Taos Route," including the purchase of land for a depot at Questa, NM, were defeated by the Great 1930's Depression. Track, rolling stock, and equipment deteriorated, losses mounted, and in 1953 the Interstate Commerce Commission authorized abandonment. Two local businessmen, W.W. "Bill" McClintock and George Oringdulph, then formed the Southern San Luis Valley Railroad to ship potatoes grown near Mesita, CO, and acquired the entire property. To replace two aging steam locomotives, they began construction of the D500 in 1954, but by its completion in 1956 traffic from the south had dropped sharply, the track was in poor condition, and derailments were frequent. By 1958 trucks were hauling the potatoes, the last steam engine had been retired, and the 29 miles of track to Jaroso had been torn up, leaving the D500 to move locally shipped ice-cooled fresh produce and volcanic scoria to the Denver & Rio Grande Western connection at Blanca. Seasonal produce and year-round scoria kept the line operating for another 20 years; produce shipments had ended by the late 1970's and scoria lasted until the early 1990's. The Southern San Luis Valley Railroad no longer exists, but 1.53 miles of its track, the Blanca Spur, remain in the San Luis Valley under the ownership of the Colorado Pacific Rio Grande Railroad, successor there to the Denver & Rio Grande Western.