The best way is right across the street (Waterloo) from Kinney Rd, where everyone parks for SSP and home of the infamous iron gate. That trail is much better maintained than the Waterloo South Trail mentioned, which was a total unmaintained POS when I went down it once a few years ago. It's a tough but makeable climb in two stages. The first stage will merely wake you up. The second stage is less kind. The Rogue trail intersects in the middle.