Draw a selection using your favorite tool (the lasso is usually easiest to work with) around where you want the lowest edges of the mountains to be. The important thing about using the mound tool is to try to make the edges a little crinkly to avoid really straight spines. You should also use the Add operation when creating the mound to allow multiple things to stack. Stacking multiple mounds will often get better results instead of just using a single mound. One mound will have a single spine, but multiple mounds can get lumps wherever they cross. You can also draw your selections with multiple parts if that helps what you're trying to get. This sample shows one mound going north/south to get the main mountain outline and a selection in multiple parts to get some crosswise parts. Note that you can paint selections in other tools if that's more your style (white = selected, black = not) and then import those images as selections using Select>>Load Selection.

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Also, 4096 isn't a particularly large editing resolution since FT3+ pushed over to a 64-bit program. However, "large" is always a relative term and it is mostly dependent on your machine. Lowering the editing resolution and increasing it later can work, but you need to be much more careful of artifacts when doing that.