William Clark was the first recorded visitor to Leary Site; on July 12, 1804, he noted in his journal:

. . . after going to Several Small Mounds in a leavel plain, I ascended a hill on the Lower Side, on this hill, Several Artificial Mounds were raised; from the top of the highest of those Mounds I had an extensive view of the serounding Plains, which afforded one of the most pleasing prospects I ever beheld, under me a Butifill River of Clear water of about 80 yards wide Meandering thro a level and extensive Meadow, as far as I could See, the [view of the] prospect Much enlivened by the fine Trees & Shrubs which [was] is bordering the bank of the river, and the Creeks & runs falling into it,- . . . I observed artificial mounds (or as I may more justly term Graves) which to me is a strong indications of this Country being once Thickly Settled. (The Indians of the Missouris Still Keep up the Custom of Burying their dead on high ground.) (Moulton 1986, 2: 369-370)

Clark correctly conjectured that these mounds were constructed for human burial. The mounds are a component of one of the largest and richest prehistoric villages of the Oneota culture.

A court martial also convened on July 12. Alexander Willard was charged with lying down and sleeping while on guard duty. The court found him guilty and "being a breach of the rules and articles of war (as well as tending to the probable destruction of the party)" he was sentenced to "one hundred lashes, on his bear back, at four diferent times in equal proportion" (Jones 2000, 3). The Corps of Discovery set out at sunrise on July 13 to continue their westward trek.

Leary Site, located near Rulo, Nebraska, is a National Historic Landmark. It is an archeological site that is not open to the public. However, a collection of artifacts from the Leary Site can be viewed online.