Mosca is an unincorporated community and a U.S. Post Office in Alamosa County, Colorado, United States. Mosca's population is 1,072 as of the 2020 census. It was named for the nearby Mosca Pass, which was named for the Spanish explorer, Luis de Moscoso Alvarado. The Mosca Post Office has the ZIP Code 81146. It is best known for its proximity to Great Sand Dunes National Park and Preserve.