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.
Among the more helpful tribal members he reported encountering was a negro who claimed to have been on Lewis & Clark's expedition, and who may have been the explorer-slave York.
At the Great Salt Lake a group led by Joseph R. Walker, including Leonard, split off from Bonneville and followed the Humboldt River, then crossed the Sierra Nevada mountains into California.
Leonard’s journal provides detailed descriptions of life in California in the Mexican period.
In 1835 Leonard returned to Independence, Missouri, with enough wealth in furs to establish a store and trading post at Fort Osage.