In 1831 he went with Gannt and Blackwell's company of about 70 men on a trapping and trading expedition. Living off the land (Leonard reported that "The flesh of the Buffaloe is the wholesomest and most palatable of meat kind"), Leonard and his associates endured great privation while amassing a fortune in furs; the horses died in the harsh winter and the party was at times near starvation. They survived, in part, by trading with Native Americans. Among the more helpful tribal members he reported encountering was a negro who claimed to have been on Lewis &amp; Clark's expedition, and who may have been the explorer-slave York. In 1835 Leonard returned to Independence, Missouri with enough wealth in furs to establish a store and trading post at Fort Osage. He continued to trade along the river for the rest of his life.