|In addition to birds, the park is home to a number of mammal species. Some of the most likely to be seen are Columbian Black-tailed Deer, Mule Deer, Snowshoe Hare, Beaver, Common Pika, Townsend's Chipmunk, Red Squirrel and Douglas' Squirrel. More secretive and less abundant mammals such as Elk and Moose are observed less frequently. Caution: Black Bears and Cougars frequent the park and may be encountered on hiking trails and in open areas.
In early summer, a loud chorus of Pacific Treefrogs can be heard in the marshlands. Several other amphibian species take advantage of the numerous beaver ponds and pools, including Western Toad, Columbia Spotted Frog, Northwestern Salamander and Roughskin Newt. Tailed Frogs are found in some of the fast moving mountain streams.
Over 20 species of butterflies can be observed along the roadway from March to September. The Ross Lake picnic area, Chittenden Meadow and Whitworth Meadow all contain plants and flowers that attract butterflies looking for nectar or for host plants on which to lay their eggs.