I was looking at the 2007 map and see that since the 3000 line is inside of the public land, it is not mentioned on the map. Neither are any roads inside of the public lands. Also, when you look at the confluence of the North Fork of the Toutle and Alder Creek, the boundary line is drawn a little down stream, but the boundary is at that junction.
Also the legal description says "South along Johnson Creek". The creek actually flows almost due west to the Toutle.