1. Trends of structures in Idaho-Wyoming Thrust belt.

2. Laramide basement uplifts containing Archean and Proterozoic igneous and metamorphic rock.

3. Late Cretaceous foreland basins.

4. Paleocene and Eocene basins.

5. Eocene lakes.

Simplified geologic map of the central and southern Rocky Mountains. The Oregon Trail crossed the Continental Divide at the south end of the Wind River Mountains, and headed west across the Green River Basin to the Idaho-Wyoming Thrust belt (heavy lines) and the Snake River Plain. From King (1977).

Used by permission of Princeton University Press.