Great Sand Dunes System

NPS/Great Sand Dunes NPP

The large dunefield is actually just one of four primary components of the Great Sand Dunes geological system. The mountain watershed, dunefield, sand sheet, and sabkha are each important aspects of this complex sand system.

 

Sand Creek Basin is part of the mountain watershed of the Great Sand Dunes, protected in Great Sand Dunes National Preserve.

NPS/Patrick Myers

The mountain watershed of Great Sand Dunes receives heavy snow and rain each year. Creeks flow from alpine tundra and lakes, down through subalpine and montane woodlands, and finally around the main dunefield. Sand that has blown from the valley floor is captured and carried back toward the valley. When creeks disappear into the valley floor, sand is again picked up and carried into the main dunefield. This recycling action of water and wind contributes to the great height of this dunefield.

 

The main dunefield is the centerpiece of the Great Sand Dunes system.

NPS/Patrick Myers

The 30 square mile (78 sq. km) active dunefield is where the tallest dunes reside. It is stabilized by opposing wind directions (southwestly and northeasterly), creeks that recycle sand back into it, and a 7% moisture content below the dry surface. The dunefield is composed of reversing dunes, transverse dunes, star dunes, and a few barchan dunes. It is estimated to contain 6.5 billion cubic meters (1.5 cubic miles) of sand.

 

The sand sheet is a mix of grasslands and small dunes surrounding the main dunefield on three sides.

NPS/Scott Hansen

The sand sheet is the largest component of the Great Sand Dunes geological system, made up of sandy grasslands that extend around three sides of the main dunefield. Almost 90% of the sand deposit is found here, while only about 10% is found in the main dunefield. The sand sheet is the primary source of sand for the Great Sand Dunes. Small parabolic dunes form here, then migrate into the main dunefield. Nebkha dunes form around vegetation.

 

Sabkha deposits around a shallow wetland

NPS/Patrick Myers

The sabkha, or alkali flats, is a strange, harsh environment containing white, powdery mineral deposits.

Sabkha develops on the lowest elevations of the valley floor where surface and ground water flow to before leaving via evaporation. The groundwater is salty, so a variety of minerals crystalize into a white crust on the ground. The most common is a baking soda-like mineral known as ‘trona’.

Areas of sabkha can be found throughout western portions of the sand sheet, wherever the water table meets the surface. On older maps, it was labeled as ‘wasteland’, as the alkalis made for a harsh environment and were not settled upon. Only salt-tolerate life can survive there. In this area are both deeper stream or spring-fed wetlands with rich plant and animal life, and shallower, salty evaporating groundwater. Shorebirds, salamanders, frogs and toads thrive in the deeper freshwater areas, but in the salty portions, only salt-tolerant life forms can survive, such as inland saltgrass and certain invertebrates.

In the late 19th century, a tiny community called Soda City sprang up beside one of the thickest deposits of alkali west of the dunes. Residents collected and packaged the soda, then carried it by wagon to Mosca, where it was loaded onto trains. From there it reached various cities where it was sold as ‘Washing Soda’.

The easiest public areas to access sabkha in the Great Sand Dunes area are San Luis Lakes State Wildlife Area, located 15 miles west of the visitor center, and Blanca Wetlands, located south of the national park on County Lane 2S.