This is a trail up to Hidden Valley Falls, up a dry underground creek by the Buffalo National River in North Central Arkansas.    The water to the falls flows out of a cave a good way up a canyon, and precedes to flow underground except during the torrential rains that sometimes strike in the spring.    The creek surfaces only to carve a 100 ft. cave, flow over a little falls into a 60 ft. pool, and then disappears again until it bubbles up in the river as a spring feed to the river.    The Cave is refreshingly cool in the hot Arkansas summer.    There is a waterfall inside the cave, that I have not yet photographed--I keep forgetting to bring my flashlight.