Idaho
Circle-irrigated fields flank the Saint Anthony Sand Dunes, which formed between ancient volcanic features.
Flying over southern Idaho, you might spot something below looking very out of place. Between circle-irrigated fields and jagged lava flows lies a surprising landscape for this area: a sea of white, fine-grained sand dunes. The Saint Anthony Sand Dunes date back to about 10,000 years ago, when this part of Idaho was much cooler and wetter than it is today.
Back then, now-extinct creatures such as woolly mammoths grazed on extensive grasslands and drank from several large lakes in the area. Two of these lakes, Mud Lake and Market Lake, still exist about twenty miles southwest of the dunes, but they are dried-up fractions of their former expanses. When the climate began warming at the end of the last ice age, around 11,500 years ago, the shorelines shrank, exposing acres of sandy deposits that had sat at the bottom of the lakes. Sand from the floodplain deposits of the Snake, Teton, and other rivers also added to the bank of sand, which began migrating north.
In order for sand dunes to form, you need a lot of sand, wind, and a place for the sand to collect. Near the present-day town of Saint Anthony, the blowing sand encountered a lava field related to the Craters of the Moon volcanic complex to the southwest. The cracks and crevasses of the cooled lava flow trapped the sand, preventing it from blowing away. On the north side of the dunes are the Juniper Buttes—extinct and highly weathered volcanoes. Trapped by the lava field, the dunes started forming against the southern flanks of the Juniper Buttes.
Today, these dunes cover 175 square miles, in an elongated swath thirty-five miles long and five miles wide, trending to the northeast. The highest dunes, rising more than 400 feet, are still actively moving at a rate of a few feet per year. Many types of sand dunes can be created by wind, but the dunes of Saint Anthony are all barchan dunes—named for the Arabic word for a ram’s horns. Barchan dunes are crescent shaped and created by winds that blow from one primary direction, with the horns of the dunes facing downwind.
From the air, the horns of the Saint Anthony Sand Dunes face northeast, primarily blown by winds from the southwest that flow steadily in the winter months. Older dunes, stabilized by plants and no longer moving, appear slightly darker on the north side of the lighter, moving dunes. The hilly formations next to the dunes are the Juniper Buttes.
Steady winds out of the southwest have sculpted the Saint Anthony Sand Dunes into crescent shapes that are still moving to the northeast.
En route to Idaho Falls or Pocatello, Idaho; Jackson, Wyoming; or Bozeman, Montana, keep an eye out for white, rippling dunes north of Idaho Falls and Rexburg, Idaho.
