Geology Along the Lewis & Clark Trail

Geologic Points of Interest

The Bitterroot Mountains

The Lolo Pass at the crest of the Bitterroot Mountains began one of the Corps' biggest ordeals. These mountains are made up of intrusive igneous granites of the Idaho Batholith. They presented formidable geographic obstacles as winter began to set into the northern Rocky Mountains. (Lewis and Clark, 9/12/1805)

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