This section of the old highway is one of the oldest roads in the state of Washington. This road was built about 1839 after the Puget Sound Agricultural Company (PSAC) began to farm on the Cowlitz Prairie. The PSAC was a subsidiary of the Hudson's Bay Company. This road was originally about a mile long an ran between Simon Plamondon's farm, the Cowlitz Mission and the PSAC farm, which was known as the Cowlitz Farms. Plamondon was a retired HBC employee who arrived at Washougal 1816 and started work for the HBC. He and retired in 1837. John McLoughlin asked him if he would settle on the Cowlitz Prairie as the British were trying to establish settlements north of the Columbia so they could make the river the international boundary. Plamondon agreed and that was the beginning of the Cowlitz Settlement.
The French-Canadian families living in the Willamette valley, petitioned in 1834 for Catholic priests. The priests were approved to come to Oregon and start a mission, but had to depend on the HBC to get them there. They agreed to transport them on the condition they build the church north of the Columbia at the Cowlitz settlement, to bolster the British presence north of the river. The church agreed to the request and Fathers Blanchet and Demers opened the Cowlitz Mission in 1839.
This road was used to get from the settlement to the church.
This section of road became the Pacific Highway in 1915 and the attached old photo was taken about a mile north of the Plamondon road.
I attached a drawing of my best attempt at a duplication of the 1853 BLM map on a Google map.