SR 503 Spur, known locally as the Lewis River Road, begins its route at an intersection with SR 503 east of Yale and north of the Yale Bridge. The highway travels northeast along Yale Lake through a forested region of Cowlitz County, passing Yale Park and the community of Cougar. SR 503 Spur turns east at Beaver Bay Park and ends shortly thereafter at Forest Route 90 on the Skamania County line south of Mount St. Helens National Volcanic Monument and Gifford Pinchot National Forest. The Lewis River Road was part of State Road 15 from 1909 until 1919 and was re-established in 1991 as a spur route of SR 503. WSDOT conducted a series of surveys to measure traffic volume in terms of AADT and calculated that 650 to 1,300 vehicles per day used the spur route in 2011.