Mountain
The Mountain runs 135 tiles wide and only 41 deep, from the quarry bridge in the east to the railroad steps in the north-west. It is shown after the repairs: the quarry bridge restored, Leo's treehouse up and the community-upgrade shortcuts open. The early-game landslide and the blocked railroad corner have both cleared in this world, so the nineteen tiles behind them are yours to plan on.
What you can place here
You can place objects, machines, furniture, fences and paths here; crops and buildings stay on the farm.
Other valley maps
Ginger Island NorthGinger Island SouthGinger Island South-EastGinger Island EastRailroadBackwoodsSecret WoodsSummitPelican TownCindersap ForestPelican BeachCalico Desert
Start a plan on any of them from the Valley tab of the New-plan picker in the planner.