Grand Prismatic Spring, the country's largest hot spring, is the centerpiece of Midway Geyser Basin. The lot is on the right for southbound drivers, with vault toilets, and parking runs short between 10 a.m. and 6 p.m. The boardwalk runs beside the spring, but the famous overhead view of the color bands comes from a different place: the Fairy Falls lot, a mile farther south, starts a 1.2-mile round trip climbing 105 feet to the overlook. The National Park Service allows one to two hours for it. The spring's bacterial mats are fragile, and damage to them can last more than a year, which is one more reason to stay on the boards. Excelsior Geyser, in the same basin, had large hydrothermal explosions in the 1880s. Biscuit Basin, farther south, is closed.
The boardwalk at Grand Prismatic starts from the Midway Geyser Basin lot, on your right in a few hundred yards. Same squeeze here from ten to six, so early or late is your best bet, and if it's full, don't wait in the road. There are vault toilets here. Want the view from above? It isn't from this lot. Go about a mile further, to the Fairy Falls lot, also on your right. From there the overlook is a one point two mile round trip that climbs a hundred and five feet, so give it one to two hours. No hot spring in the United States is bigger, and few in the world are. A trapper named Osborne Russell got here in eighteen thirty-nine and left what's probably the earliest written account of any thermal feature in Yellowstone that can be definitely identified. He called it a boiling lake about three hundred feet across, described steam in three colors, and left the explanation to some scientific tourist. Science did turn up. Those rings of color are bacterial mats, the mats that give the spring its name, and damage to them can take more than a year to repair. Life that loves heat turned out to matter a long way from here. Out of hot water came Thermus aquaticus, the first organism recorded surviving above a hundred seventy-six degrees. One of its heat-resistant proteins became the irreplaceable piece of the genetic method called P. C. R. Up the road, Biscuit Basin is closed, lot and boardwalk both. Ask at a visitor center before you count on it. Turn right out of the lot. The next big name on this road is Old Faithful.
Photo: NPS Photo / Jim Peaco · Public domain