We need the option to "Naturalize" the terrain in an area so that it restores it to its original state and doesn't cause the need for it to be tracked in memory anymore so that, when you're done terraforming, you get less performance issues by "Naturalizing" any overflow areas that didn't need any terraforming after all, or, when you're done working in an area and you want it to go back to it's original state… Naturalize.
ie. Fill holes left in mountains/copper craters/trenches.
This would be very helpful because, even if you raise/lower the land to be as close to normal as possible, currently, it will still use memory since it is still technically modified.
I think it should also require resources so that it has less chance of becoming exploited for purposes that it is not intended for.