Lewis and Clark Pass crosses the continental divide at the crest of the Northern Rocky Mountains which lie to the west of the Cascade County Square Butte. From that pass on July 7, 1806 the explorer Meriwether Lewis (of the Lewis and Clark Expedition, 1803-1806) returning eastward from his journey to the mouth of the Columbia River and the Pacific Ocean, saw Square Butte on the skyline of the eastern Montana prairie stating in his journal:2 m. passing the dividing ridge between the waters of the Columbia and Missouri rivers at 1/4 of a mile [Lewis and Clark Pass]. from this gap which is low and an easy ascent on the W. side, the fort mountain [Square Butte] bears North Eaast, and appears to be distant about 20 miles. From that pass on a clear day, the Cascade County Square Butte can still be seen, not at the 20 miles reported by Meriwether Lewis but about out in the eastern Montana grasslands.