This is the approximate location of the (KINCAID) Cave Opening, it is likely rocked up and made to look natural now, there was a tramway which ran over the top of the opening. The Tramway was taken out around 1956, but notice the adit 700 Yards to the N/E AT ONE TIME when the canyon floor was about 1000 feet higher the entrance likely looked "SIMILAR" to this following image,
The opening today is about 1400 feet below the rim, I wonder what a drone camera would reveal...
However a massive flood from the North washed the anterior away leaving only a cave opening and washed out near 1000 feet of the bottom of the canyon, this "May" have been TWO separate incidents.
With River rafting becoming an increasing sport, plans were made to flood the canyon again with the intent to further wash down chunks of broken pillars, statues and other evidences of identifying sculptured rocks which were abundant along the river banks from the site and all the way to the curves near bright Angel... Of course this artificial flood of the 1990's was of course "said" to restore the sand bars of the river... Remember the restrictions areas where you could not go ashore? This may still be in effect...
Location of the Tram and Towers in 1954 before being removed
1954 USGS Topo
1956 Topo, one tower left
Later Map, tower is gone but Adit Appears... why?