Couloir comes to us from France, where the word’s primary meaning is “corridor.” Since the eighteenth century, however, the term has also been applied to vertiginous mountain gullies. In October 1872, upon cresting a divide in the Sierra Nevada, John Muir observed (in The Mountains of California): “There, immediately in front, loomed the majestic mass of Mount Ritter, with a glacier swooping down its face nearly to my feet. . . . The entire front above the glacier appeared as one giant precipice. . . . The head of the glacier sends up a few ﬁnger-like branches through narrow couloirs; but these seemed too steep and short to be available, especially as I had no axe with which to cut steps. I could not distinctly hope to reach the summit from this side, yet I moved on across the glacier as if driven by fate.” A few hours later, after nearly falling to his death (“I became nerve-shaken for the ﬁrst time since setting foot on the mountains, and my mind seemed to ﬁll with a stiﬂing smoke”), Muir emerged from the top of one of these sheer couloirs to make the ﬁrst ascent of 13,157-foot Mount Ritter.