As it turns out, there is no cliff at the tubing park. It bears no resemblance to a cliff at all.
Also, one cannot flop on their belly there as to do so would risk serious facial injury from the hard-packed snow walls of the tubing slides.
There was virtually no risk involved in sliding down the hill -- at least not unless another patron managed to follow too closely behind and hit you. I didn't see that happen even once, so I doubt it's a common source of injury. Common enough to be included on their posted list of risks, though.
There were 2 fairly risky spots though. One was the gentle downward slope from the end of the tubing run to the people mover. That would have been safe, except for the children who insisted on coasting toward the conveyor on their tubes without regard to the safety of other patrons and apparently with the blessing of their parents - or at least with their tacit consent.
I did find a very quick way to put an end to that. Threat of physical injury, even by small children, does not bring out the best in me.
"If you knock me over, I'm going to make a point of landing on you. I don't believe you'll enjoy that very much."
Either the kid would wise up or the parents would snatch them away before they managed to topple me.
The second danger spot was the conveyor-belt style people mover. Again, unsupervised, or marginally supervised children insisted on engaging in risky behavior immediately in front of or behind me. After asking politely for them to desist -- to no effect, I employed the tone of voice I generally save for first year residents who say things like "In my experience....." Works just as well on kids.