Historians and doctors of today believe that Charles Floyd, the only man who died during the Lewis and Clark Expedition, passed as the result of appendicitis and the eventual rupture of his appendix, for which there was no cure in 1804.  He would have died even if he'd stayed home.  His burial site is in modern day Sioux City, Iowa, where he is commemorated with a monument that looks the same as George Washington's, only significantly smaller.