Thanks! I looked at my favorite world maps for that inspiration, like Hero's Realm, Dragon Warrior, and Ultima. Using 2k3 mountains as hills then 2k mountains as proper mountains but recolored so they stand out as distinctly unpassable was something I noticed from Hero's Realm and recreated. Good use of RTP assets!
If it was Ace I might've made the hills also slow walking too, for maximum DW1 vibes.