This is a vintage Sawyer's View Master reel from 1948 titled, "The Black Hills of South Dakota U.S.A" #203. It is marked with its patents and has a white back.
Reel 203 contains: Sylvan Lake, Pigtail Bridge Iron Mt. Road, Mt. Rushmore Memorial by Borglum, Homestakes Gold Mine Richest in USA, dinosaur park above rapid city, devils tower 1280 Ft above river, and Wild Game in the Black Hills.
This reel is in Very good pre-owned condition, measures 3.5" in diameter and comes in a sleeve.