Guttermouth Gulch is road intersection in Oregon. It is nothing more than a small area with two roads and tight squeezed with surrounding cliffs. One leading to Pond Dungeon and another leading to Assassins' Creek. A road sign can be found here, and many bears spawn around this area.
The in-game music will also change when the player wanders around this area, especially right after using a roadsign to travel to this area.