Nestled against the western slopes of the Sangre de Cristo Mountains of south-central Colorado are the tallest sand dunes in North America. Covering 30 square miles and rising to 750 feet in height, the dunes are the centerpiece in a collection of diverse ecosystems. In 1932 the dunes and the surrounding areas were protected as Great Sand Dunes National Monument, but in 2004 the area was redesignated by Congress as Great Sand Dunes National Park and Preserve.
The dunes themselves have been growing and shifting for hundreds of thousands of years. In that time sand from the floor of the San Luis Valley has been carried eastward by the prevailing winds. As sand-laden wind reached the Sangre de Cristo Mountains and slowed it dropped the sand in this natural trap. Over the millennia the sand accumulated here, continuously building dunes that migrated toward the mountains.
Today enough vegetation has established itself in the valley to make the dunes relatively stable. Little new sand is added to the dune field, but within the field individual dunes continue to shift and migrate.
My wife and I visited this park for about six hours last week. While we were there most people were gathered around the dunes themselves, eager to climb up the impressive mountains of sand. In spite of the name this park is more than just “great sand dunes,” however, and we were eager to see what else could be found here. In addition to the dunes this park encompasses rivers, grasslands, shrublands, wetlands, montane and subalpine forests, and alpine tundra. We were able to visit several of these diverse ecosystems in our limited time.
Throughout much of the year Medano Creek runs down from the mountains along the eastern edge of the dune field. In mid-summer, however, water was completely absent from the creek bed:
In spite of the dry creek, moisture-loving plants could be found along the banks. Most noticeable were the sandbar willows (Salix exigua, Salicaceae) and narrowleaf cottonwoods (Populus angustifolia, Salicaceae):
Other shrubs, herbs, and wildflowers also decorated the areas around the dunes:
In particular the bright, light purple flowers of Rocky Mountain beeplants (Cleome serrulata, Capparaceae) added swaths of color the the landscape:
After my wife went to take a nap I decided to hike up the Mosca Pass Trail. This rocky 3.5 mile path gains about 1400 feet on its way up the Sangre de Cristo Mountains. It was once a popular route for Native Americans and pioneers to enter and exit the San Luis Valley.
Early on some trees like these quaking aspen (Populus tremuloides, Salicaceae) provided a bit of shade:
Before long the trees began to thin out, giving way to some sun-loving herbaceous plants like this scarlet gilia (Ipomopsis aggregata, Polemoniaceae)…
…Wyoming Indian paintbrush (Castilleja linariifolia, Scrophulariaceae)…
…threetooth ragwort (Packera tridenticulata, Asteraceae)…
…narrowleaf yucca (Yucca glauca, Asparagaceae)…
…and prickly pear cactus (Opuntia sp., Cactaceae):
The views back down toward the San Luis Valley got more and more impressive with altitude:
In some places rocky outcrops on the trail provided opportunities to look back down on the dune field:
While the namesake dunes of Great Sand Dunes are certainly an impressive sight to behold, there is much more to this park to be discovered. We got a decent look at the diversity on our brief visit, but with many more miles of trails and different ecosystems to explore, a longer visit would certainly be welcome.