Thanks for all the nice compliments...they are much appreciated.
The bridge was created by the collapse of a lava tube, which is the reason for all the rubble at the bottom. You can just barely make out this debris in the orbital photo of the feature. There are a number of collapsed lava tubes on earth (notably in Hawaii) which provided visual models for this depiction. It's also similar to the enormous piles of rock one finds under large domes in caverns.