I'm too busy to post anything detailed today. I have to work my regular job and chip away on my novel.
In the meantime, here's an image I'd meant to post earlier. We encountered this at Welch Spring. There was a small "closed" sign in the spring itself. Seemed strange until I realized that you could dive into the water, go through the spring outlet and emerge into an extensive cave system just beyond.
The Park Service does not want you to do this. For the following reason: