This is the Needles Cave feature near Calico Rock. It's a horseshoe shaped bluff-lined hollow that hides three caves...one which has reportedly been mapped verydeep (5 miles). The horseshoe is a good 200-250 yards across at the open end and about as deep. This place is truly awe-inspiring and has a rich history which I may get to share as I've been invited to hear some of the yarns about the place next time we get over that way.
So...watch this space.
And here's a short vid-clip to give you a grain of an idea of the magnificence of the place!
I want to give a word of thanks to the landowner, who graciously allowed our eager little crew to view this special spot in Izard County...heck...the world!
I also want to give a hat-tip to BBanzai, who told me about the cave.