DD had the same problem. The quest list is wrong. If it is saying you have the waterfall, it means you have the rock. She went back and took a pic of the waterfall (even though the list showed she had that one and not the rock) and BINGO, she got her Gold Oswald. This seems to be a glitch only in the Exporer's Tent on the Quest List. Thanks to another DISer's suggestion, we figured out the problem.