While exploring the Louisiana Purchase with Lewis and Clark, he took ill at the end of July 1804. On July 31st, Floyd wrote in his diary, "I am verry sick and has been for Sometime but have Recovered my helth again." However, this apparent recovery was soon followed by a severe turn for the worse. William Clark described Floyd's death as one "with a great deal of composure" and that before Floyd died he said to Clark: "I am going away. I want you to write me a letter."
A funeral was held and Floyd was buried on a bluff overlooking the Missouri River. The expedition named the location Floyd's Bluff in his honor.
Clark diagnosed the condition which led to Floyd's demise as bilious colic, though modern doctors and historians agree Floyd's death was more likely to have been caused by a ruptured appendix. The brief "recovery" Floyd described may have represented the temporary relief afforded by the bursting of the organ, which would have been followed by a fatal peritonitis. If that were the case, because there was no known cure for appendicitis at that time, he would have been no better off had he been with the best physicians of the day.
After Floyd's expedition journal was published in 1894, new interest was taken in him and his gravemarker was stolen by thieves. He was re-buried once more on August 20, 1895 with a monument. A marble cornerstone three feet wide and seven feet long was placed in 1900. When the obelisk of white sandstone standing 100 feet (30 m) high was completed on May 30, 1901, Floyd's grave was moved for the fourth time to rest nearby, where it remains to this day. In 1960, the monument was recognized by the U.S. Department of Interior as the first National Historic Landmark. It was designated a National Historic Landmark on June 30, 1960.[1][2]
