The Great Sand Dunes are North America's tallest dunes, a 30 square mile complex in the San Luis Valley at the base of the Sangre de Cristo mountains.

The Great Sand Dunes have a 7% moisture content below the dry surface

The sand dunes hold only 10% of the total sand deposit; the rest lies in the Sand Sheet

Native Americans ground Indian Ricegrass seeds into flour, which was prepared in various way

Avalanches occur when moving sand exceeds the angle of repose

Vegetation stabilizes the surrounding Sand Sheet, neutralizing expansion

Mountains form an impassable barrier that traps blowing sand at its base

Spadefoot toads emerge from the sand after spring rains for a brief season of life above ground

Opposing winds blow sand back onto itself, which accounts for the dunes exceptional height

Mule deer can detect water up to 2' below ground, a vital attribute in this arid climate

Melting snow brings torrents down Medano Creek each spring

The sand dunes have settled in a low pocket beneath the Sangre de Cristo mountains

Saltation describes the bouncing of individual grains of sand

Plants grow long roots to draw moisture from the dunes

Blowout grass looks similar to Indian ricegrass, but lacks the characteristic black rice seed

The tallest dunes rise 750' from a base elevation of 8,140'

Narrowleaf cottonwood are a good indicator of where water may pass

The sand dune complex includes transverse dunes, reversing dunes, star dunes, and barchan dunes

Rich shrub and grasslands around the dunes support deer, elk, and pronghorn

Star dunes form only in places where wind blows from different directions over the course of a year

Autumn is an ideal time to visit, with moderate daytime temperatures and cool but not too-cold evenings

Rabbitbush - one of the most ubiquitous plants in the park - blooms late summer and well into fall