"We saw a herd of buffaloe come down to water at the sulpher spring this evening," Lewis recorded on the eighteenth of June, 1805. "I dispatched some hunters to kill some of them, and a man also for a cask of mineral water."
Location of Bison Spa
Mouse over image to see labels
The vegetation on the banks today might not have been present when Lewis passed by. The trampling of buffalo herds watering at the hole would have kept it from growing as thickly as it appears above, if at all.
The bison, of course, would have contributed one or two more odors to the mix.