Grand Prismatic Spring

The center of Grand Prismatic is a deep, clear blue, the color of very pure, very hot water, near boiling as it rises from below. That water is too hot for most life, which is why the middle stays a sterile, brilliant blue.

As the water spreads outward and cools, it enters temperature bands where different heat-loving microbes can survive, and each builds a mat of a different color. Cooler outer rings glow orange and rust with pigments the microbes make to shield themselves from the sun, warmer inner rings turn yellow and green, and the result is the ringed rainbow that gives the spring its name. The colors are richer in summer sun and fade toward green in the cooler, lower-light months.

Yellowstone sits atop one of the largest volcanic systems on Earth, a hot spot where molten rock lies relatively close to the surface. Rain and snowmelt sink deep, are heated, and rise back up through cracks, feeding the park's thousands of geysers, hot springs, mud pots, and steam vents. Grand Prismatic is simply the grandest of the springs.

The whole Midway Geyser Basin steams and hisses around it. The runoff from the spring pours over broad orange terraces down to the Firehole River, and Excelsior Geyser Crater, a giant collapsed spring, pumps thousands of gallons a minute into the river nearby. It is a place where the raw machinery of the planet is on full, quiet display.

A boardwalk loop from the Midway Geyser Basin parking area leads right out across the terraces and along the edge of Grand Prismatic. Up close you feel the heat and see the vivid microbial mats, though from ground level the steam often hides the full shape of the pool.

For the postcard view, the one that shows the whole rainbow eye at once, take the short but steeper hike to the Grand Prismatic Overlook, reached from the Fairy Falls trailhead just to the south. It climbs a forested hillside to a platform looking down on the spring, and it is worth the extra walk.

Long before it was a park, this country was known and traveled by many tribes, among them the Shoshone, whose Tukudika or Sheepeater bands lived in the Yellowstone high country. Their descendants and other tribes retain deep ties to this land.

Bison often graze the warm ground and thermal meadows near the basin, and it is vital to keep well back from them. Elk, bald eagles, and waterfowl move along the Firehole. Summer is warm, crowded, and best for the colors, while spring and fall are quieter, cooler, and often steamier. Roads through this part of the park close in winter, when the basins can be reached only by guided snowcoach or skis.

The closest Boutel™ stays, so you can turn this stop into an overnight. Each is an independently owned, editorially selected place to stay.