I ride Bby Mtn regularly with my son and i find that a full suspension bike with 130'ish mm of travel front and rear should do the trick for the blues and even Gear Jammer/Upper Cut/Lower Snake a partial black rated trail.
I have ridden the above noted trails above as well as Dead Moped/North Road trail with my 2000 Norco Sasquatch steel hardtail with a 125mm front fork without any issue so if you like a challenge a 100mm plus travel hardtail will work.
More importantly, i think the appropriate tires and brakes must be considered. In my opinion, having good disc brakes and trail specific tires are a must.
Budget is key - if you can only afford a low spec full suspension, it may be better to buy decent hardtail. 2yrs ago i was borrowing my friends 06 giant faith before buying a giant stance - and from there making my bike more descent oriented.
Depends on what your budget is. I personally of the mindset of getting a higher end hardtail then a low end full suspension.
Also if your not adverse to picking up a used bike you might be able to find something. A friend of mine just picked up a Commencal hardtail which he has been really happy with.... mind you he only picked it up this year, so not allot of KM's on it yet.