Mosca Pass, elevation , is a mountain pass in Alamosa and Huerfano counties in the Sangre de Cristo Range in southern Colorado. The pass lies on the eastern border of the Great Sand Dunes National Park and Preserve about 40 miles west of Walsenburg, Colorado. It marks the boundary between the Great Sand Dunes National Preserve to the west and San Isabel National Forest to the east, and it also lies on the border between Alamosa and Huerfano counties.