Lewis's Tower Mountain
By his estimate, on June 5, 1805, Meriwether Lewis was 38 miles up the Marias River from the Expedition's camp on the Missouri. Looking northward, he saw "a lofty single mountain which appeared to be at a great distance, perhaps 80 or more miles. . . from it's conic figure I called it tower Mountain." It is now called the West Butte of the Sweet Grass Hills, which are igneous intrusions into the surrounding sedimentary Cretaceous rock, standing northeast of Shelby, Montana.
Lewis's estimate of its distance from him was closer when he entered his courses and distances for that day, on June 8: He wrote "about 60 miles." It is actually just under 60 miles from Lewis's probable location. He had already remarked that the clear air of the high plains made it difficult to estimate distances.
During the 1920s the Sweet Grass Hills were the scene of intensive oil and natural gas production.