I'm no Columbia expert by any stretch. But there's good water all through there, all the way up to I-5 and beyond. Rod holders and a fish finder will be pretty key. Even an el-cheapo fish finder at least gives you depth and bottom contour. I think the higher and cooler the water, the closer to the banks the fish run. And a Columbia River anchor with tons of rope and a buoy.
Once you get out there and drive around, you'll see the hotspots. Don't hogline until you've mastered anchoring. Talk to others about anchor systems -- generally, you'll use a carabiner to attach the anchor to the bow, so you can quickly drop OFF it and chase the fish, then go reattach to the short line that goes between the buoy and the boat.
Lots of good water around Government Island. And it's no big secret to lower your gear down to the ends of the wingdams, because the fish have to go around them.
And when sitting on anchor, ALWAYS keep an eye upstream for floating debris like logs and whatnot. If a large log rolls up on your anchor line, you're swimming, and go home with one less boat in your possession. Keep a sharp knife near the anchor mount, and be ready to undo the carabiner at any time.
Be friendly, and the Old Timers out there will show you stuff.