Snake River Canyon
Near Twin Falls, Idaho
The ground opens without warning here. One moment you are on flat high-desert farmland, and then the earth drops five hundred feet straight down into the Snake River Canyon, a basalt-walled chasm that bisects southern Idaho like a scar left by something ancient and violent.
The canyon is, geologically speaking, exactly that. The Snake River Plain sits atop a hotspot track, the same volcanic conveyor belt that now powers Yellowstone, and over millions of years successive lava flows built up the plateau. The river, meanwhile, carved steadily downward, exposing layer after layer of basalt columns, some formed twelve million years ago, others as recently as two thousand years back. The walls you see from the rim are a cross-section of Idaho's volcanic biography.
But the most dramatic episode came roughly fifteen thousand years ago, during the last ice age. Lake Bonneville, a vast ice age lake in what is now Utah, burst through its natural dam at Red Rock Pass and unleashed the Bonneville Flood, a megaflood that geologists estimate moved at roughly forty-five miles per hour. The water scoured the Snake River system with a force that widened the canyon, sculpted the waterfalls downstream, and left behind the chaotic broken terrain visible today across southern Idaho.
The canyon's walls average four hundred to five hundred feet in height in the Twin Falls reach, dropping to the river that is itself one of the most heavily dammed waterways in North America. Fourteen dams along the Snake's main stem transformed the river from a salmon highway into a controlled irrigation and hydropower system. Salmon once ran up the Snake as far as Shoshone Falls, just downstream, feeding the Shoshone-Bannock for centuries, but dams downstream now block them.
The rim above you has become one of the few places in the world where you can legally jump off a bridge and land safely. Every year, hundreds of BASE jumpers launch from the Perrine Bridge spanning the canyon at the town's north edge, a legal, year-round jump that has made Twin Falls famous in a community where the canyon has always defined what this place is.
