I finally made it there again and got a screenie with locators. Methinks that goto mound1 is the entrance to the cave, but is not working. http://dl.dropbox.com/u/76702168/POTC screenies/Sand Bluff trigger.jpg
I have managed to get a couple of the screenies by Shark Bait from post 59. ( copied the links into a new tab in iexplorer)
I have tried to mark where I think the place is where you fall into the cave - it is on the flat ground on one side of the small hill ( I have tried to mark it in the image with a red circle - but I am going from memory here ).
In the cave ( which is like the Barbados cave in the jungle you fall into it in a different place ) go and find the ladder which is the exit - then follow the instructions in post 59 to find the treasure chest.
I have attached a Map - not sure how clear it is.