Complex sentence: Its southern and southeastern boundaries are surrounded by the Fraser River and the Interior Plateau while its far northwestern edge is delimited by the Kelsall River at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains.
Split into simpler sentences: Its southern and southeastern boundaries are described by the Fraser River and the Interior Plateau. Its far northwestern edge is delimited by the Kelsall River at the north end of the Alaska Panhandle, beyond which are the Saint Elias Mountains.