The highway is legislated to begin at a junction with SR 410 in Greenwater, in eastern Pierce County. The road would travel east along the historic Naches Trail, passing through Mount Baker-Snoqualmie National Forest and across Naches Pass to Wenatchee National Forest. It would terminate at another junction with SR 410 north of Cliffdell in Yakima County. The highway would pass near Pyramid Peak, which has a maximum altitude of . A crossing similar to the legislated highway is covered by a series of Forest Routes, including Road 19 and Road 70.