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January 24, 2023

House Rock, a massive boulder in the Gallatin River, has a long history.

House Rock is an enormous feature in a section of the Gallatin River called the Mad Mile. At high flows, thrill-seekers are drawn to the Class IV rapids—and to the risk. Dead Man’s Alley, a section below House Rock, is not hyperbole. The Mad Mile drops 98 feet in one mile, with 13 rapids churning past limestone cliffs. Pinball, Snaggletooth, and Two Scoops are all warm-ups for the crux that is House Rock that splits the river, creating the most technical section of the Mad Mile. When the water is high, this is where rafts capsize.House Rock is also a favorite barometer for local weather watchers. When the river is rushing over the top of House Rock, like it did last June, it’s officially flooding. Cue the House Rock footage on the local news. In the 1880s, the Gallatin River was used to float railroad ties downstream. For the loggers tasked with moving the timber, it was a “thrilling adventure… with sharp projection rocks appearing at intervals in the boiling waters.” Log jams at Cave Creek—the pioneer’s name for House Rock—were commonplace. The rock was renamed decades later by whitewater rafters and kayakers— because it is house-sized. In the late 1800s and early 1900s, House Rock served as pilings for a pole bridge for livestock. Historical photos show large boulders around the rock that are no longer present. In The Gallatin Way to Yellowstone, Duncan Patten uses a series of photos to suggest House Rock itself may have moved downstream in the last century, likely during a period of high flows in 1974, and possibly again in 1997. “It may well have moved a short distance in flood events,” says Mary S. Hubbard, an earth sciences professor at Montana State University. “But its irregular shape suggests it did not travel a long distance, otherwise it would be more rounded.” Technically, House Rock is a quartzofeldspathic gneiss, likely a part of the more than two billion-yearold “basement” of southwest Montana, says Hubbard. “It likely ended up in the valley due to rockfall.” Geology and boating aside, anglers are more interested in low water. “When the water’s high and dirty, the fish have trouble seeing the flies,” says Drew Hay of Gallatin River Guides. In late summer when water levels are low and water temps are higher, rainbow and brown trout congregate around House Rock. “It’s really oxygenated in there because of all the rocks,” Hays says. “But House Rock is more meaningful to the whitewater community. For fly fishers, it’s just a big rock.” For the rest of the Big Sky community, past and present, though, House Rock is a landmark and an icon—smack dab in the middle of a Mad Mile.To read the full article, click here.

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