This tumbling mountain stream situated on the eastern edge of the maritime climate of the Pacific Northwest, the Lake McDonald Valley marks the extreme eastern limits for western hemlocks and red cedars, hence the rain forest feel of Avalanche Creek. The humidity in this valley allows red cedars to grow to heights of 100 feet, and diameters of 4 to 7 feet. and foster the lush green of ferns and mosses growing along the forest floor. The moss-covered boulders, and a rushing stream of glacial water of Avalanche Creek creates a unique canyon on the Avalanche Lake the is the real water source of the creek.
The red rocks are part of the Grinnell Formation, a stack of lightly metamorphosed sedimentary rocks up to 2,600 feet thick. Iron oxide the rocks creates the red hue that stands in stark juxtaposition to the green of the forest.