The State mammal of Oregon is the American Beaver. It is also the national animal of Canada.
A large semi-aquatic rodent, it lives in ponds, streams, rivers, and lakes. They are know for creating a debris dam and lodge in creeks, thus creating a flat water habitat for fish, fowl and more. A beaver can take down a 10 in/25 cm tree in just a few hours.
This happens to be south of Salem, but can be seen in many parts of the state.
The flag of Oregon is unique, it has the escutcheon from the state seal on one side, and an illustration of a beaver on the reverse. (Wikipedia)