20,000 Bison

Lewis had seen great "gangues" of bison on more than one occasion—an estimated 3,000 near Oacoma, South Dakota, in September of 1804, 10,000 at the Great Falls of the Missouri on July 1, 1805.

South of the White River, near today's Chamberlain, South Dakota, on August 29, 1806, he beheld an awesome sight.

I assended to the high Country and from an eminance I had a view of the plains for a great distance. From this eminance I had a view of a greater number of buffalow than I had ever Seen before at one time. I must have Seen near 20,000 of those animals feeding on this plain.