The Longview Kelso branch of PSH 12 traveled 5 miles east from an intersection with the Ocean Beach Highway, signed as PSH 12 and U.S. Route 830 (US 830), onto Nichols Boulevard around Lake Sacajawea and Tennant Way in Longview and crossed the Cowlitz River to Kelso, where the highway ended at an intersection with the Pacific Highway, signed as PSH 1 and US 99.