The City of Alamosa is a Home Rule Municipality that is the county seat and the most populous city of Alamosa County, Colorado, United States. The United States Census Bureau estimates that the city population was 8,682 in 2005. The city is the commercial center of the San Luis Valley in south-central Colorado. Alamosa was established in May 1878 by the Denver and Rio Grande Railroad and quickly became an important rail center. The railroad had an extensive construction, repair and shipping facility in Alamosa for many years and headquartered its remaining narrow gauge service here with trackage reaching many points throughout southwest Colorado and northern New Mexico. Alamosa is now a notable tourist town with many nearby attractions including the Great Sand Dunes National Park and Preserve. The town hosts a SummerFest on the Rio which occurs the first weekend in June and the Early Iron car show over the Labor day weekend. The city takes its name from the Alamosa River. "Alamosa" is a Spanish adjective meaning "of cottonwood".