On 6 August 1804, Sgt.
Patrick Gass found the one fossil known to survive from the expedition today. He did not mention it in his journal (nor did either of the captains in their journals), but the data were recorded by Lewis on a tag that accompanied the specimen to
Philadelphia. It accompanied the so-called
Fort Mandan shipment, the first batch of specimens to be sent back East from
Fort Mandan, in 1805. Gass's
discovery was near Soldiers River, which flows in Harrison County, Iowa, in (we know now) strata dated to the Cretaceous Period. The original label indicates that it was collected in a "cavern," but this is more likely to have been an undercut in the stream bank rather than an underground passage.
Lewis and Clark - Fossils