Skull Rock Waterfall is a waterfall on N. Sanity Island carved into the shape of a skull in a mountain. So far, it has made several appearances throughout the series, but all are very minor.
The waterfall makes a brief appearance in the level select map, where it seems to be the source of the level Upstream.
Skull Rock Waterfall can be briefly seen from the Secret Warp Room on N. Sanity Island.
The waterfall makes a brief appearance in the intro, where it is attached to the mountain in the middle of N. Sanity Island.
The waterfall now plays a much larger role in this game, where it is on N. Sanity Beach. Due to the island's massive evolution, it now creates a pool of water connected to the ocean. Beside it is a water spout, which is launching out fish constantly. Also, Farmer Ernest's farm is located behind the waterfall. There is a giant hole underneath the skull's mouth.
Though this isn't the N. Sanity Island one, there is a big skull waterfall in the track Tiki Turbo just after the shark jump. Ebenezer Von Clutch most likely designed it like that to resemble the original N. Sanity Island skull as he designed the whole park based on his hero, Crash Bandicoot.
It reprises the roles it had in the first and second games.