State Route 123 (SR 123) begins at an intersection with U.S. Route 12 (US 12) northeast of Packwood, in the Gifford Pinchot National Forest. Paralleling US 12 and the Ohanapecosh River, the highway crosses Boulder Creek and enters a canyon where the roadway encounters Forest Route 44 (FR 44), a connector from SR 706 to Mount Rainier National Park. The segment of SR 123 in the heavily forested canyon is the busiest along the road, with a daily average of 803 motorists in 2007. Still in the canyon, the roadway exits the Gifford Pinchot National Forest and enters the Mount Rainier National Park. The roadway enters Pierce County from Lewis County and passes the Ohanapecosh Visitor Center, located above sea level. SR 123 crosses Laughingwater Creek and passes Silver Falls and the entrance to Steve Canyon to the trailhead of the Grove of the Patriarchs Trail. Now following the Chinook Creek, the highway travels into a tunnel under Seymour Peak and ends at an intersection with SR 410 at Cayuse Pass.