On August 12, 1805, Meriwether Lewis wrote of reaching "the most distant fountain of the waters of the mighty Missouri" after many difficult days and sleepless nights. In 1921, historians named this spring "Most Distant Fountain," identifying it as the water source Lewis referred to in his journal. Lewis described water issuing from the base of a low hill about 1/2 mile below Lemhi Pass, but whether he was writing about this spring may never really be known. The spring forms when water from rain and snowmelt seeps into the ground, pools above solid layers of rock or clay in an aquifer, and then flows back to the surface, often along fault lines or fractures underground.