I think that is the second loop (coming from the west). If it is, the picture was taken from right about where the newer highway is today.
Stephen, I thought there was a pullout viewpoint on loop 2 though. There’s a lot of trees blocking any view
I didn't know there was a viewpoint there. Judging from how it looks now, I didn't notice any place where it looks like there was room to pull over. But it is pretty overgrown now, and hard to even follow the old road around the curve. There's definitely a lot more trees in this picture compared to the old postcard pictures, but maybe a lot of trees grew by 1952? Looking at historicaerials.com, it looks like there was quite a few trees surrounding all the loops in 1951. I was also guessing loop 2 because of the shadows make me think this picture was taken in the afternoon, with the camera pointed to the northeast. And also, the other loops didn't appear to drop off so much on the outside of the loop.
Stephen, yeah, I might be wrong about the viewpoint. I could’ve sworn I had an old picture of cars parked there. And yes the trees definitely grew between those times
Kirk J. Poole, February 9, 2021:
I haven't seen anything yet that indicates enough width for a pullout, unless it's just downhill from Loop 4...