We didn't know it at the time but this was the remains of the Winona Mill site.

http://cali49.com/jtnp/2014/12/8/the-winona-mill By 1945, a "large mill" here was idle, owned by a man named R.A. Theobald. It reportedly had a capacity of 40 tons per day and was powered by a 40-horsepower Buick motor. The Winona Mill performed custom milling for the small mining operations located around Cottonwood Spring.