The Chehalis River flows out of the Douglas Ranges of the Coast Mountains in the southwest corner of British Columbia, near Chilliwack, running south-eastward before draining into the Harrison River.

Though its valley has been heavily logged, the river itself passes through a small canyon before a flatter stretch leading to its confluence with the Harrison. The Chehalis is valued both as a fishing stream and a whitewater destination.

Together with tributaries such as Statlu Creek, it offers Class III and IV kayaking. Access to the river corridor is typically via Morris Valley Road off Highway 7 at Harrison Mills, with gravel forest service roads extending further into the watershed.