This is the Davis Motor Mine cart.
This "Davis Motor Mine Cart" is a home built creation using most of a 1926 Harley-Davidson 21 ci. B Model motorcycle.
The machine also features a Ford Model-A transmission with electric start and was used to pull wagons of ore out of an underground mine. It was recovered from an abandoned Northern California gold mine in 1970. Now is part of an exhibit of the Harley-Davidson Museum.