Local folklore myth, drawing on the lives of real people, but the article has their names muddled up. They weren’t Dr. William Frisbee and Dr. J. Lewis, but Dr. William Frisbie and Dr. William F. Lewis, who were cousins. Dr. John Lewis was not an adjoining property owner… he was the father of William Lewis, but he died when William was a youngster.
After moving away and returning to Mankato in the spring of 1862, Dr. William F. Lewis went into a pharmacy partnership with his cousin Dr. William Frisbie who had located there the previous summer. After three years, Lewis pursued a career in banking until October 1886 when he then spent most of his time travelling.
It’s highly unlikely that these two well-educated men would have buried a significant quantity of Black Walnut logs for filling in a gully. Even by the 1860s, the highly prized wood was in short supply and, by 1875, the local furniture companies of D. S. & G. V. McGraw, and Charles Heilborn had bought up nearly all the black walnut lumber and timber within hauling distance of Mankato, paying top dollar for it. The failure of the local supply was one of the causes for the McGraw business closing in 1879.
[Ref: Mantako: It’s First Fifty Years – Free Press Printing Co, 1903]