This image shows the boarding ramp of the car ferry named the City of Munising. It operated across the Straits of Mackinac after being renamed from Pere Marquette 20 where it operated between Ludington, Michigan and ports in Wisconsin.
The description states:
THE CITY OF MUNISING
Michigan State Ferry preparing to dock air Mackinaw City, Michigan. S 65
–The cars indicate that this image is likely from the 1950s.