This arch is a needle's eye that is more slender and interesting than the famed Needle's Eye on the Needles Highway.
The above arch is in the Cathederal Spires formation.
Natural Bridges in the Black Hills:
True -- There are at least nine natural bridges in the Black Hills. The locations are not widely known. (Allegedly there are actually twelve, but we have only been able to confirm only nine.) The Eye of the Needles along the Needles Highway in Custer State Park is one.
Edit 7/29/2014: The geocachers have identified this arch.