There's an artifact NEAR the forked waterfall on top of the pillar next to it. In fact, there were a few alien eggs on top of various pillars in the elf region.

My last 2 artifacts that I had trouble finding were the one at the back of the ship (been up there several times, but never all the way back, and it is fairly well hidden back there) and 1 on the back of the island where you fight the guys with the light sabers.