Believe me there is enforcement of it, just not much. A study done by an independent group in 2008 found that Yakima County should have 7 WDFW Officers, Kittitas should have 5, well both counties have 3 officers. DNR is also suppose to patrol the area, but the DNR Officer based in Kittitas county has a patrol area consisting of 15 eastern WA counties, and he is the only DNR Officer for those 15 counties. WDFW does make cases for these violators every year, but a lack of personnel is the big problem, not a lack of will to enforce it.
I know all the WDFW guys in that area, and they would love nothing more than being able to catch the trespassers. Unfortunately, they don't have the manpower to "camp" on the area and wait for a violation. If some of the guys on this site have some names, vehicle descriptions and plates, and even better if you know when they're going to be in the closure, they would be there to get them. The best cases WDFW Officers make often times come from good tips from the field.
If you don't want to do it yourself, pm me with GOOD info (the more specific the better) and I'll make sure they will get it.
