This valley serves as a home and retreat for the sasquatch dwelling in the Cold Frontier. While their bands range far and wide, this is where they raise their young. In all likelihood they will quickly become aware of any intruders, but stay out of sight - though the explorers might hear their howls or wood knocks from time to time, or catch a whiff of their musky scent.
More problematic are the strange monsters prowling the valley, especially the phantom fungi. The sasquatch know enough about how to avoid them, but explorers will be stalked for hours until one of them gets separated from the rest. These invisible attackers should be especially terrifying when they suddenly strike out of the mists.