When you look at this area in the edit mode, there are strange overlays of National Forest, long diagonal lines connecting boundaries of polygons that were likely incorrectly drawn. I don't have the slightest clue where to start on fixing this. The whole Mt. St. Helens National Volcanic Monument boundaries and are are quite incorrect. It should probably be deleted and started over, but it's a large project that shouldn't be left to someone with my knowledge.