A Story of Water, Fire, and Time
If you’ve ever driven through Tecopa or Shoshone, you’ve probably noticed those soft-looking, whitish hills with almost nothing growing on them. They’re odd, a bit ghostly, and different from the rocky desert around them. These are the crusted ash hills, and, believe it or not, they tell a story that spans millions of years—a story of an ancient lake, distant volcanoes, and a massive drain that changed everything.
Once Upon a Time… There Was a Lake
About 2.5 million years ago, this part of the Mojave Desert wasn’t dry and dusty like it is now. Back then, a big lake—called Lake Tecopa—filled the valley where the town of Tecopa sits today. It wasn’t deep like Lake Tahoe, but it was wide and full, fed by streams and the Amargosa River. The climate was wetter, and the area around the lake would’ve had animals, birds, and maybe even trees and marshes in some spots.
Rain of Ash From Distant Volcanoes
While the lake sat quietly for thousands of years, volcanoes far away—in places like Yellowstone and eastern California—were blowing their tops. When they erupted, clouds of ash blew across the skies and fell into Lake Tecopa. This happened multiple times, and each time the ash settled to the lake bottom, mixing with mud and silt from the hills.
Over time, the lakebed became layered like a giant cake—mud, ash, mud, ash. Some of these ash layers originated from eruptions so powerful that the entire western U.S. was covered in dust. One layer is from the Yellowstone supervolcano, another from the Long Valley Caldera (near Mammoth). These layers still show up today as bright white stripes in the hills.
A Salty Soup of Mud and Minerals
Because Lake Tecopa had no outlet, the water just sat there and slowly evaporated, leaving behind salts and minerals. This made the water somewhat like soup—salty and full of unusual ingredients. That “soup” transformed the ash into clay and minerals, such as sepiolite (a slick, soapy clay) and even tufa, a crusty white rock that forms from spring water rich in calcium. You’ll still find tufa lumps sticking out of the hills today.
The Great Drain
Everything changed about 150,000 years ago. Either the lake overflowed or the Amargosa River carved its way into the basin, but somehow the water finally found a way out. In just a short time—maybe weeks or months—Lake Tecopa drained away, cutting a canyon (now called Amargosa Canyon) and flowing downhill toward Death Valley. The lake never came back.
After that, the land dried up, and wind and rain started eating away at the soft lakebed. The hills we see today began to form as water carved out gullies and the sun baked the surface into a hard crust. That’s why the ground looks cracked and salted—because it is. Underneath the crust, you’ve got layers of ancient mud and ash that have been sitting there for hundreds of thousands of years.
What It Looks Like Now
Today, these ash hills are quiet and strange. They’re mostly bare—almost nothing grows on them because the soil is salty and crusty. After a rare rain, you might see tiny salt crystals form on the surface. When it’s dry, the hills flake and crumble under your feet. Some are rounded; others are capped with gravel that protects them from erosion, like little hats. Those protected hills often appear darker due to desert varnish, a type of shiny black coating that forms over thousands of years.
If you’re walking out there (carefully), you might find fossil footprints from when this was a lakeshore. Horses, camels, and even mammoths once strolled through this muddy basin before it dried up. Then a layer of volcanic ash buried their tracks, perfectly preserving them like a snapshot in time.
Why It Matters
These crusted ash hills are like pages from an ancient book. Scientists can read the layers and learn about ancient climates, massive eruptions, and how the Mojave Desert evolved into its current state. They also remind us that even the driest desert places were once full of water—and that everything on Earth, even quiet hills, has a story.