Geology Along the Lewis & Clark Trail

Geologic Points of Interest

Lewis Overthrust

At Camp Disappointment, Lewis could see the Marias River's headwaters in the mountain range to the west (now known as the Lewis Range) (A). The range was created when the Lewis Overthrust placed Precambrian rocks over Cretaceous shales near the end of the Cretaceous 65 million years ago. This fault is well exposed at Marias Pass (B). (Lewis, 7/26/1806)

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