Brower’s Spring is a small spring in the Centennial Mountains of southwestern Montana near the Continental Divide, remembered for Jacob V. Brower’s claim that it is the ultimate headwaters of the Missouri River and thus of the larger Mississippi–Missouri river system. Brower identified the site in 1888, argued for it in his 1896 book, and in 1895 buried a copper plate nearby that has never been found. His proposed source lies farther upstream than the source Meriwether Lewis identified in 1805 near Lemhi Pass. Though not officially recognized in the Geographic Names Information System, the spring endures as an important geographical and historical claim.