Great Sand Dunes National Park and Preserve

Listen first. The wind moves across the open valley, and the sand answers with a dry, steady hiss. Under your feet the ground gives a little with every step. Ahead of you, a wall of pale gold dunes rises against dark mountains. In the morning the ridges are sharp and clean. Their shadows fall in long blue curves. For a moment the scale makes no sense. These dunes look like they belong to a desert on another continent, yet you are standing in southern Colorado.

This is Great Sand Dunes National Park and Preserve, at the eastern edge of the San Luis Valley. The valley is a wide, high basin. It is far larger than it looks from here, and the air is thin because the ground already sits high above the sea. Behind the dunes rise the Sangre de Cristo Mountains. The name is Spanish for the Blood of Christ. Locals often say the peaks turn red at sunset, and on a clear evening you can see why.

Here is the first surprise. These are the tallest sand dunes in North America. The highest, known as Star Dune, rises more than two hundred metres from its base. That is taller than many city skyscrapers. From the parking area the dunes seem close and modest. They are neither. Distances here fool the eye, because there are no trees, buildings or people on the sand to give you a sense of scale.

So where did all this sand come from? Geologists trace much of it to the San Juan Mountains, far to the west across the valley. Over a very long time, rivers and streams carried sediment down into the basin. Ancient lakes once filled parts of the valley floor. As those lakes shrank, they left behind wide beds of sand. The wind then went to work on them.

The main winds here blow from the southwest. They pick up sand from the valley floor and push it toward the mountains. The Sangre de Cristo range acts like a barrier. The air must rise to cross the low passes, and as it slows, it drops its load of sand. But strong storm winds also blow from the opposite direction, down through the mountain passes. These two forces push the sand back and forth. Instead of spreading out, the dunes pile up higher and higher.

Now look at the sand closely, if you can. It is not one colour. You will see light grains mixed with dark ones. Many of the dark grains contain magnetite, an iron mineral. Some visitors bring a small magnet and drag it through the sand. Black grains jump up and cling to it. In places, the wind sorts these heavier grains into dark streaks along the ridges, like lines drawn with charcoal.

Between you and the dunes, in late spring and early summer, runs Medano Creek. The snow melts in the mountains, and a shallow, wide stream spreads across the sand. Families wade in it and children build sand castles, as if at a beach far from any ocean. And here is the second surprise. The creek often flows in pulses called surge flow. Small ridges of sand form underwater, then collapse, and little waves roll downstream. By late summer the creek usually shrinks or disappears.

People have walked this valley for thousands of years. Archaeologists have found evidence of early hunters who followed herds of animals here. In more recent centuries, the Ute and Jicarilla Apache peoples knew this land well. In the forests at the edge of the park, some old ponderosa pine trees carry long scars where the bark was carefully peeled away. These culturally peeled trees are linked to Native American use of the inner bark for food and medicine.

Later travellers arrived from the east and the south. In 1807, the American explorer Zebulon Pike crossed the mountains with his men and saw the dunes. He wrote that they looked like a sea in a storm, frozen in place. Settlers, ranchers and miners followed through the nineteenth century. Some even tried to mine the sand for gold. Local residents later pushed to protect the dunes, and the site became a national monument in 1932.

The area gained national park status in the early 2000s. The change protected much more than the dunes themselves. Today the park and preserve stretch from wetlands and grasslands on the valley floor, up through forests, to alpine tundra and lakes near the mountain summits. In a single day, a strong hiker can move through several very different worlds. Few places in the country hold so many landscapes so close together.

Life on the dunes is tougher than it looks. Summer sand can become dangerously hot by the afternoon, hot enough to burn bare feet. Yet small creatures live here. Kangaroo rats survive without drinking water, getting moisture from the seeds they eat. Some insects live nowhere else on Earth, including a tiger beetle found only in this dune field. Watch the sand in the early morning. You may see tiny tracks left by animals that moved through the night.

When night comes, the park changes again. Far from big city lights, the sky here is very dark. The park is recognised as an International Dark Sky Park. On a moonless night, the Milky Way stretches above the ridges like a pale band of smoke. Some visitors climb the dunes in the evening simply to sit and watch the stars appear. The sand cools quickly after sunset, so the air can feel cold even in summer.

Now turn back toward the dunes in front of you. Notice how the ridges are never quite the same twice. The wind reshapes the crests every day, and your own footprints will fade within hours. The mountains behind them have stood for ages. The sand between them is always moving. As you walk away, listen once more to the soft hiss of grains crossing the ground. The dune field is still being built, right now, one small grain at a time.