Well, a quick search for 'rocky_desert' in files gives this:
- descr_daytypes.txt
- descr_grass (though not applicable for rocky_desert)
- descr_settlement_plan (for battlefield vegetation)
- descr_sounds_enviro.txt (for ambient sounds)
- descr_sounds_stratmap.txt (for map sounds)
- descr_vegetation.txt (for battlefield vegetation)