US 12 continues south concurrent with I-5 through Chehalis and Centralia before exiting again at exit 68 south of Napavine. The highway then heads east along the Cowlitz River and passes through the town of Mossyrock, where it intersects SR 122. East of Mossyrock, US 12 runs just north of Mossyrock Dam and Riffe Lake. In the town of Morton, it intersects SR 7, which heads north to Tacoma. It then ascends the Cascade Range, passing south of Mount Rainier, and intersects SR 123, which serves the Stevens Canyon entrance of Mount Rainier National Park. Twelve miles (19 km) east of this intersection, US 12 crosses the Cascades over White Pass at an elevation of . White Pass is the only crossing of the Cascades open year-round between I-90 over Snoqualmie Pass and SR 14 through the Columbia River Gorge.