Rockiness
From Alpha Centauri Wiki
Each square on the map can fall into one of three categories of Rockiness: flat, rolling, or rocky.
Flat regions produce no minerals unless a mine is build there. Rolling regions produce a single mineral, Rocky regions also produce 1, but produce 3 with a mine or 4 with a mine and road.
Rocky areas inhibit movement, costing twice the normal number of moves to enter. Units on them have a +50% defensive bonus in combat.
A base may not be founded on a rocky square, terraform LEVEL with a Former first.
Ocean squares produce minerals only if you build a mining platform, in which case they produce 2.
