| Boulder River | |
| Pushpin Map: | Washington#USA |
| Pushpin Map Size: | 300 |
| Pushpin Map Caption: | Location of the mouth of the Boulder River in Washington |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Washington |
| Subdivision Type3: | Region |
| Subdivision Name3: | Snohomish County |
| Length: | 14miles |
| Source1: | Craig Lakes |
| Source1 Coordinates: | 48.1872°N -121.6981°W |
| Source1 Elevation: | 3888feet[1] |
| Mouth: | Stillaguamish River |
| Mouth Coordinates: | 48.2819°N -121.7875°W |
| Mouth Elevation: | 325feet |
The Boulder River is a river in the U.S. state of Washington.
The Boulder River originates in the Cascade Range, from the slopes of Three Fingers, Mount Bullen, and Whitehorse Mountain. It flows northwest and then northeast through a portion of Boulder River Wilderness to join the Stillaguamish River. The Stillaguamish empties into Port Susan, part of Puget Sound. The river's source is the Craig Lakes, two remote lakes located high on the slopes of Three Fingers. After exiting the lakes the river plunges over Craig Lakes Falls as it descends into the Boulder River Wilderness.
The river flows northwest from there and just as it is turning northeast it tumbles over very bouldery Boulder Falls. The river also flows over one more waterfall, Half Mile Falls, before the river makes its final push toward its confluence with the North Fork Stillaguamish River.[2]