Hello FedTonyHD,
first of all try to open TheIsland Map and try to look how WildCard have done there stuff and what Material they Used for the Landscale.
Normal you have a base Material for Landscapes “MI_NewIsland” the Second material is for Making Holes in the landscape (For caveantrance) -> “MI_NewIsland_Hole”
Did you make your Landscape in your Mainmap File ? If yes make an own Sublevel for it.
Here is a Link for the Sublevel structure of WildCard https://wiki.arkmodding.net/index.php?title=Sublevel