The mouth of Little Cottonwood Canyon is littered with enormous boulders of granodiorite and granite sitting on metamorphic bedrock that is over a billion years old.  These boulders, called glacial erratics, were transported down the canyon by the ice and left behind when it melted.

The lateral moraine on the north side of the mouth of Little Cottonwood Canyon is covered with glacial erratics. These boulders are out of place, hence the term “erratic”.

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