On the westward leg of their expedition to the Pacific Ocean in 1805, Lewis and Clark were unaware of the pass, but by the time of their return they had learned of it from local tribal people and were determined to travel over it. On July 1, 1806, at
Traveler's Rest on Lolo Creek in the
Bitterroot Valley, Lewis and Clark split into two separate parties. Lewis was to go directly east, using the pass to take a shortcut out of the mountains to the eastern Montana plains. He then planned to veer north to explore the upper
Marias River Country before returning to the
Missouri River and descending it to where it was joined by the
Yellowstone. Clark would cross over from the Bitterroot to the
Big Hole River and then follow the Big Hole and the
Jefferson River down to the
Three Forks of the Missouri. Here Clark planned to turn east up the
East Gallatin River until he could cross over to the Yellowstone River, which he would then follow down to the Missouri where he intended to find Lewis. On July 3, 1806, Lewis left Traveler's Rest with nine men and his dog
Seaman. His route to the pass lay through the Hellgate area, where
Missoula is now located, and up the
Clark's Fork of the Columbia. He then turned and followed the
Blackfoot drainage to the pass over continental divide. After crossing the pass he then went down the
Dearborn River to the Missouri, and then out onto the plains where the
buffalo roamed. On July 7, 1806, late in the day, Lewis and his small party came to the top of the divide between the Blackfoot River and the Dearborn. Lewis described it as "the dividing ridge between the waters of the Columbia and Missouri rivers". Lewis said little about the area other than that he could see in the far distance, on the skyline of the eastern Montana plains, the landmark now called Square Butte which the Corps had dubbed "Fort Mountain" the previous July. Square Butte can still be seen from the pass on a clear day at a viewing distance of about 40 air miles. The goal of the Lewis and Clark Expedition was to find the shortest pathway from the Missouri River drainage to the Columbia River drainage. After crossing Lewis and Clark Pass, Lewis confirmed that the route that went over Lewis and Clark Pass, and then over Lolo Pass farther west, was the most direct route from the Missouri River to the Columbia River Valley. ==The only roadless pass on the Lewis and Clark Trail==