PSH 17 (Trunk)
PSH 17 was part of the first highway authorized by the Washington State legislature. The highway dated back to 1893, four years after statehood, and was originally designated by name only, not by number. When the PSH numbering system was first used in 1937, PSH 17 started at Jct PSH 16 at Twisp and headed upstream along the Twisp River to Twisp Pass, then downstream along Bridge Creek to the Stehekin River, then upstream along the Stehekin to Cascade Pass, then downstream along the Cascade River to Marblemount, where PSH 17 ended at Jct SSH 17A.
The road from Twisp to the eastern vicinity of Twisp Pass was opened to traffic. The road over Twisp Pass and along Bridge Creek to the Stehekin River was not. Some maps show a rough road extending along the Stehekin to Cascade Pass. It is unclear to me if this road was ever maintained by the state, however. The Cascade Pass to Marblemount road is open to traffic. It appears that the bridge across the Skagit River at Marblemount was built by the state in the 1930s as part of PSH 17 or the Cascade Wagon Road.
In 1949, the route of PSH 17 was changed by the state legislature. The eastern terminus was moved to Jct PSH 16 at Mazama. The highway was routed across the Cascades via Washington and Rainy Passes to Marblemount. Those portions of the older route of PSH 17 that had been opened to traffic were turned over to the county governments and federal agencies such as the forest service. Much of the earlier route of PSH 17 had not been built .
In 1961, PSH 17 was transferred to an expanded PSH 16 . In 1964, this portion of PSH 16 became SR 20, the designation still used today. The highway across the North Cascades was not actually completed until September 1972.
PSH 17 (unnamed branch)
A branch of PSH 17 began at PSH 17 near the confluence of Bridge Creek with the Stehekin River. This PSH 17 branch extended downstream along the river to the community of Stehekin. When the PSH 17 trunk was rerouted in 1949, this branch of PSH 17 was dropped from the state highway system. Today, the former PSH 17 branch is owned by the federal government and is within the Chelan National Recreation Area.
Primary State Hwys Secondary State Hwys