Ok so last night I was going all Bear Grylls and exploring. Turns out you can actually leave the playable map area and end up in a zone where there’s no rocks only trees and hills with a smooth mountain texture rather than boulders etc. Nothing at all spawns in the area. Took me about an hour or so of running around to find my way back to civilization.
Not sure if this is intended or because of plans to enlarge the map area but your giant mountains at the edge of the map are easily climbable by zigzagging up the almost vertical faces.