It's real stone. Many buildings in Detroit and Michigan - some now lost - were built with stone in that time. Certainly several of the city's churches were.
Oh, and who thought this was a motel and why? It was always a residence as far as I know. Part of a 'garden apartment' movement that was more popular in other cities and built to resemble residential courts and terraces in Britain. My mother lived nearby on Brooklyn as a girl and knew kids who lived there.
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