Mountain Peaks- Ice (duh)
Islands- Water (duh)
Valleys- Earth (the ground of valleys is very fertile)
Eyesonia/Fool's Gold Border- Dark (FG is skerry)
Protoland- Holy (The man who started it all! The only place excluded is my Castle)
Castle Ansemmy- Fire ('cuz we are flamin' up in here)
Open Fields- Wind (Tornado alley is all farmland)
Anywhere a Storm may be brewing- Lightning (we don't have Thunder Plains)

In other words, Lightning is random. Unless anyone can make a better place.

Also, feel free to create more arenas.