Fat with rain, the Chehalis River howls over Rainbow Falls — “Slōsid,” or “fish trap,” these ancient fishing grounds were named. Across the highway are the last old growth trees in this half of the …Fat with rain, the Chehalis River howls over Rainbow Falls — “Slōsid,” or “fish trap,” these ancient fishing grounds were named. Across the highway are the last old growth trees in this half of the …