The McGrew Trail is awesome. Even if you just follow the dirt road to the Sourdough Camp or the North Fork Smith River Day Use area, its a nice trip. If you copy paste these into Google Earth it will give you the directions:
"Smith River" lat=41.9291691941, lon=-124.144200323
"Sourdough Campground" lat=42.0219329959, lon=-123.96654354
The town of Smith River is on the 101 just before Oregon, and it give access to the smoother ride to Sourdough (The McGrew Trail - is on the Oregon side and is rougher). It will take you every bit of an 1 and a half that it says in Google Earth. Bring your trunks the water is frosty, but crystal clear and worth the long off-shoot.
Hope that helps.
If you feel real froggy, you can go up into Obrien, OR (The trail head for McGrew) and go up into the mountain that way. I wouldn't do it without a buddy though or a good map, there are trails everywhere. You might be able to get a good map from Cave Junction information center (just north of Obrien). Have fun, just went there this weekend, such a great time - a real piece of heaven.
Matthew