Annual precipitation ranges from 3.6 to 4.2 m (12 to 14 feet). Summers are relatively dry, but only by comparison to the rest of the year. The late fall, winter and spring floods cause the Hoh River to regularly erode its banks, change its course, and deposit fresh terraces of alluvium that are soon colonized by Red Alder. Giant trees topple into the river increasing the diversity of aquatic habitats.
The dominant species in the rain forest are Sitka Spruce and Western Hemlock; some grow to tremendous size, reaching 95 m (over 300 feet) in height and 7 m (23 feet) in circumference. Coast Douglas-fir, Western Redcedar, Bigleaf Maple, Red Alder, Vine Maple, and Black Cottonwood are also found throughout the forest.
The Hoh Rainforest is home to a U.S. Park Service ranger station, from which backcountry trails extend deeper into the national park. A short, popular trail near the visitor center is the Hall of Mosses, which gives visitors a feel for the local ecosystem.