This image is an example of the kind of swimming possible in a lake so saturated with salt that one can easily float like a cork without any effort at all. The threads and perforations indicate that once there was a small bag of salt attached to the card.
The Great Salt Lake has receded and refilled a few times since this image was made, and it is unlikely the buildings shown are still in use. The famous Saltair resort was the most active venue along the lake, and has seen many ups and downs.
The description states:
Great Salt Lake, located 15 miles west of Salt Lake City, is the largest of its character in the world. The water is about 22% solids and one may float upon its surface without effort. Thousands of tons of salt, obtained by solar evaporation, arer produced annually by the industries on its shores.
–This card, like the others in the same series, dates from the 1940s.