This image shows one of the dams that form the lakes making up Pine Lake State Park in Iowa. This is obviously Lower Pine Lake dam, as it has a road passing over it, and Upper Pine Lake dam has only a trail.
There is no description on the back of this card.
The dam no longer has this appearance. Though built in 1922, it was modernized and the design significantly changed in 1991. However, the roadway remains in the same location. This image likely dates from the 1930s.