The stonework that greets the visitor to the park at the upper levels of the falls is masterfully crafted, and judging by the similarity of the blocks to one another, I would assume this is quarry-harvested stone.
The walls are handsome and seem quite formal for what amounts to a rural setting. This rounded wall terminating in a wrought-iron fence would not be out of place at a castle.
I believe CCC crews tried to use local material whenever possible. This formal wall terminates near the creek, where the native limstone is apparent. The native stone is more irregular in shape and slightly darker in color.
This is one of the stairways leading from the upper park down to the areas below the falls (along the creek). For this stairway, the sidewalls and columns appear to be of native material.
Better seen in this closeup view of the wall of the stairway. It takes more skill to create a wall out of differently sized pieces like this than the wall at the top of this post.
Our trip now brings us down to the lower reaches of the park, where the slopes along the creek are held up by retaining walls, also crafted from local limestone. This section is rather nicely done:
This wall was probably assigned to new trainees, because the limestone slabs are at irregular angles, and the mortar is much thicker, but it has served its purpose for 80 years..
In a number of places in the park the walls have started to deteriorate - an inevitable consequence in a climate where fall and spring bring freeze/thaw cycles.
A quick websearch yielded thousands of photos of Minnehaha Falls itself, but few of the stonework (which is one reason I've created this blog). Some of the better pix of stonework are these of another staircase, the bridge over the falls, the WPA retaining wall and hiking path along the creek, another staircase, and the bridge over the creek below the falls.