Reading the Rocks
The view from Olmsted Point includes a slew of glacial erratics. Photo by Grant Ordelheide
Signs of Yosemite’s glacial past are everywhere. Follow these tips on what to look for and where to find them.
Glacial erratics
Boulders that were once carried by glaciers, then haphazardly deposited across the landscape
Where: Olmsted Point
Chatter marks
Gouges left on irregular granite surfaces by moving ice or large boulders; usually on the down-canyon side of a dome or slope
Where: Lembert Dome
Glacial polish
Patches of shiny surfaces on granite that were wiped clean by moving glaciers; often located on the up-canyon side of a dome or rocky slope
Where: Pothole Dome near Tuolumne Meadows or along Tioga Road across from Olmsted Point
Subglacial water polish
Glacial polish that appears fluted or sculpted and was formed by water flowing long ago beneath the ice sheet of a glacier
Where: Pothole Dome
Exfoliation
Eroded landscape characterized by descending layers of rounded cracks; picture a peeled onion
Where: Along Tioga Road west of Tenaya Lake
Yosemite Cathedral Lake and Cathedral Peak with Glacial Nunataks. Photo by Steve Dunleavy (Flickr: Cathedral Peak, Yosemite National Park) [CC-BY-2.0], via Wikimedia Commons
Nunataks
Mountain peaks that were high enough to escape advancing glaciers, which left their jagged, sawtooth peaks intact
Where: Cathedral Peak and the Clark Range
Kettles
Small lakes in scooped-out depressions that were left by melting glaciers
Where: Gaylor Lakes and Dana Meadows
Subglacial pothole on Pothole Dome. Photo Public Domain
Potholes
Dry, bowl-shaped depressions that were carved into granite slopes when the rock was gouged by stones swirling around in melting glaciers
Where: Pothole Dome (of course)
Hanging valley
A tributary of a main river channel or valley that was down-cut faster by glacial activity than the main channel, leaving the tributary glacier higher and “hanging.”
Where: Bridalveil Fall
Roche moutonnée
An asymmetrical ridge that was smoothed by glaciers. These granite formations are often mistaken as domes.
Where: Lembert Dome
