The Suhalla Range is a large range of mountains in Gondowan.
The range essentially divides the continent into its two vertical halves, both in cultural terms and in gameplay terms. Branches of these mountains also surround the Suhalla Desert. The Suhalla Gate is a pass through them that more-or-less connects the desert to the area where Venus Lighthouse and Lalivero are. The town of Suhalla just to the north of the desert shares the name of the mountains also, and the range separates Idejima from the mainland of Gondowan through a small cave connected to the pass of Suhalla Gate.
The involved mountains' official name can be assumed to be the "Suhalla Range" based on how Alex calls them by that name in the scene at the beginning of Golden Sun: The Lost Age where an earthquake generated by Venus Lighthouse tears a rift through the mountain range, physically detaching Idejima from the base of the mountains (and causing Idejima to float out to sea).