Narrow-leaf cottonwoods are large, shady trees along riparian corridors through montane and grassland areas. Some of the largest cottonwood trees in the park have been dated at over 300 years old.

Rocks at Mosca Creek are unique and between the Sangre de Cristo fault and the east-side boundary fault, erosion has exposed a structural window beneath another fault, called the “Mosca Creek thrust.” This thrust is correlated with other thrusts south of Carbonate Mountain and at California Peak and north of the head of Garden Creek.

The geology Mosca Creek  exposes red sandstone, siltstone, and shale of the lower member of the Pennsylvanian Minturn Formation, which is about 300 million years old. In addition to its red color, the lower member contains distinctive quartz pebbles and granules that set it apart from the rest of the Minturn Formation. It is never more than about 1,000 feet thick.

This trail follows a small creek to the summit of a low pass in the Sangre de Cristo mountains, winding through aspen and evergreen forests. American Indians and early settlers used this route for travel into the valley.

The Mosca Pass Toll Road was developed in the 1870s, and stages and the mail route used it regularly through about 1911. That year, the western portion was badly damaged in a flash flood. Partially rebuilt at times in the 1930s through the 1950s, it has been repeatedly closed by flooding and is now a trail for hikers.

Credits and Sources:

“Geology Along Mosca Pass Trail, Great Sand Dunes National Parks and Preserve, Colorado,” United States Geological Survey and National Park Service. http://pubs.usgs.gov/circ/1374/Circular1374.pdf, Accessed on June 28, 2015.

“Great Sand Dunes: Hiking and Backpacking,” National Park Service, http://www.nps.gov/grsa/planyourvisit/hiking.htm, Accessed on June 28, 2015.

“Great Sand Dunes: History and Culture,” National Park Service, http://www.nps.gov/grsa/learn/historyculture/index.htm, Accessed on June 28, 2015.

“Great Sand Dunes: Plants,” National Park Service, http://www.nps.gov/grsa/learn/nature/plants.htm, Accessed on June 28, 2015.