Cut Bank Creek, like the Two Medicine River, flows from the billion-year-old Precambrian Belt rocks, 2,000 feet thick, that comprise the mountains known since the 1890s as the Lewis Range. The mountains to right of center are in today's Glacier National Park. The supposed site of Lewis's camp on July 22-25, 1806, is on the left (south) side of the creek, left of center in the photo.
From their camp on the north fork of the Marias River, now called Cut Bank Creek, Lewis dispatched George Drouilliard and Joseph Field to hunt. Reubin Field stayed with the captain.
I directed Drewyer who went up the river to observe it's bearings and the point at which it entered the mountains, …this he did and on his return I observed the point at which the river entered to bear S 50 [degrees] W. distant about ten miles the river making a considerable bend to the West just above us.
That cinched it. The Marias did not originate north of the 50th parallel. Besides, neither hunter had any success, and provisions were low. They just managed to get by on one small trout, a few passenger pigeons, and a little mush of biscuitroot. "As if the fates were against me," Lewis complained, his watch stopped. Nevertheless, he stayed where he was for two more days, hoping to make observations from which to determine the latitude and longitude of the place he was to dub "Camp Disappointment."