The Sand Sheet is the largest component of the Great Sand Dunes geological system, holding almost 90% of the deposit's sand mass. The sand sheet wraps around the base of the dunefield and extends for miles into the San Luis valley. Persistent winds from the southwest carry sand from the sheet to the Sangre de Cristo mountains, which traps sand at its base.

Mule deer chew cud, a secondary form of mechanical digestion, to facilitate digestion

Chinese walls form on the tops of <i>reversing</i> dunes

The sand sheet is stabilized by thick, low-lying vegetation that attracts an array of wildlife

Transverse dunes, common along the south boundary, are distinguished by long-running ridges

Medano Creek frames the dunefield's east side and dissipates into the sand sheet to the south

The Park's tallest dunes form along the east side where Medano Creek's deposits are heaviest

Pronghorn are crepuscular, meaning most active at dawn and dusk

Parabolic dunes form where strong winds erode sections of vegetated sand

Despite the appearance of grazing, mule deer are primarily browsers

The San Luis Valley, about the size of Connecticut, is one of the largest high desert valleys in the world

Nebkha dunes (also known as coppice dunes) are simple dunes that form around vegetation

Surface temperatures in the Great Sand Dunes can reach 140 degrees

Burrowing owls can be found in grasslands that cover the sand sheet

While there's little to prey upon in the dunes, predators frequently cross outer edges of the complex

In early summer, Medano Creek floods the east side of the main dunefield

Parabolic dunes migrate toward the main dunes on the south edge of the complex

The San Luis Valley measures 125 miles long and 65 miles wide

Vegetation traps windblown sand, enabling plants to grow taller

The Sangre de Cristo mountains have over thirty five 13,000'+ peaks

Most of the sand sheet is veiled by grasslands that extend for dozens of uninterrupted miles