Although this was a very popular spot at South Mountain in the past, it's almost unknown to the general public now. On any given Saturday when there are hundreds of people on National trail you can visit this area and be alone for hours even though it's only 50 yards off National...it's just that well hidden. Surprisingly, even though it was an official attraction at one time with reinforced (CCC?) trails leading up to it, it's off the maps now.
Here's a section of the Official 1964 South Mountain Park brochure map showing Natural Bridge near the Natural Tunnel. Note that Mormon Loop trail is missing because it hadn't been created yet. Also Fat Man's Pass was called Wonder Rift on this map.
At that time it was one of only a handful of pictures in the Park's brochure:
Here's a picture from when my family visited it in 2006:
Too bad it's not on the maps any more, it's a really neat place to visit.
As requested here are directions to the Natural Bridge. Please do not approach from National Trail, that approach is closed for revegetation. The approach from Hidden Valley was part of the original official trail (look for small CCC work on part of trail near bridge) This approach does not have any signs showing the old trail as being closed.
CLICK ON IMAGE FOR LARGER READABLE MAP
To get onto the old trail, make a left just before running into "spaceship rock" (so named by my family since it resembles an approaching Star Destroyer from Star Wars) on the Hidden Valley trail just after exiting the tunnel. (This picture was taken facing south)
The old trail (facing north) is lined with many small rocks.