I don't get nervous very often when we are hiking/exploring (unless I'm standing on the very edge of a big drop); but seeing all this rock that had recently fallen and then standing directly underneath this arch was starting to make me a little uneasy.

Let me describe what you are seeing.  There are basically four "layers" of rock here. The first is the cliff wall to the left of the arch.  The middle two are the two layers of the arch.  The one on the right is the back wall--you can see it is lit up more from the light coming in from above, behind the arch.