The Tower / Lamar reach is the probable Yellowstone River crossing on the return arc of the loop. The modern Grand Loop Road links Tower, Lamar, and the Northeast Entrance — the practical auto-route closure before exiting via Beartooth (US-212) or Chief Joseph (WY-296).
The Lamar Valley — locally known as the 'Serengeti of North America' for its modern wildlife concentrations — was a critical seasonal hunting ground used by Crow, Blackfeet, Shoshone, Bannock, and Nez Perce. The northeast quadrant of the park is where the densest Indigenous archaeological evidence has been documented.
The Yellowstone-Lamar drainage was a corridor between the plains-edge trade at Fort Raymond and the higher interior trapping country. Colter's return path almost certainly used pieces of this drainage to close the loop back toward the Bighorn.
Modern Grand Loop Road carries traffic between Tower Junction (Roosevelt area), the Lamar Valley, and the Northeast Entrance toward Cooke City, MT. The byway connects to the Beartooth Highway (US-212) and the Chief Joseph Scenic Byway (WY-296). Colter's reconstructed return arc plausibly used this drainage; the specific path is low-confidence.
Whether Colter crossed the Yellowstone River in this reach, further upstream near Tower Fall, or somewhere outside what is now park boundary. The geometry is plausible; the specifics are not recoverable from the surviving record.
The Tower Junction / Roosevelt Lodge area and Lamar Valley are accessed from the park's Northeast Entrance (Cooke City) or via the Grand Loop. Mammoth Hot Springs is the major developed area to the west. The Northeast Entrance road links directly to Beartooth (US-212).
Phase 3 target: drone footage of the Lamar Valley plus 360° at Tower Fall, paired with the Beartooth/Chief Joseph route closures.
Sources & attribution: NPS Yellowstone · Yellowstone Forever · Merrill J. Mattes (NPS, 1962)