cave excavations

The type of soil here and I bet out there[sand] an excavation would be better made from at or near the top of a ridge than at the base.Unless it is made in the underlay of sandstone bedrock that is exposed and in cliffs in a few places.Perhaps near the surface but not showing at ground level and of course and maybe most likely from underwater and then up.Underwater is where most of the sandstone would be accessible to our boy.And the toughest["impossible maybe"]for a searcher to find,perhaps that is why a den has not been found.