The Pacific Crest Trail from Mexico to Canada was created by connecting established trails. In Washington that trail was the Cascade Crest Trail which ran the length of the state. The CCT was officially established in 1938 by the Forest Service and the YMCA. The earliest route map I have seen is from 1937. Much of today's PCT route is the same as it was in 1937. Here I discuss only the parts that have had significant changes since then. On any page, right-click the map to open it full-size in a new tab.
Section L - Hopkins Lake to Canada
Section L - Rainy Pass to Harts Pass
Section K - Red Pass to Suiattle Pass