In A Walk in the Woods: Rediscovering America on the Appalachian Trail, Bill Bryson wrote: “I never met a hiker with a good word to say about the trail in Pennsylvania. It is, as someone told a National Geographic reporter in 1987, the place ‘where boots go to die.’ . . . Mile upon mile of ragged, oddly angled slabs of stone strewn about in wobbly piles. . . . These require constant attentiveness if you are not to twist an ankle or sprawl on your face—not a pleasant experience with ﬁfty pounds of momentum on your back.” Such a hiker on the Appalachian Trail in Pennsylvania might just as well have been complaining about nivation hollows. A bowl-shaped depression in the ground, a nivation hollow begins to take shape when ice forms over a shallow rock basin beneath a snow bank. The ice freezes and thaws over time. During the warm period, melted snow seeps into the bottom of the hollow. During the cooler period, the seep water freezes. The rock breaks up, weathers, and erodes. Meltwater carries away the ﬁner rock particles and the hollow becomes larger and deeper.