Welcome to OFF.
I'd suggest the Sandy and / or the Clackamas. But, again, they're not open yet for trout. Both streams have springers and summers. But, a 5 wt. rod is IMO too "light" for such bruisers.
Get yourself a copy of "The Complete Angler's Guide to Oregon", or "Fishing in Oregon" (new revision coming out sometime this Spring, according to the author). Those books are the Bibles of fishing around here. You'll learn a lot, in a short amount of time on where to go, what species, run timings, directions, etc.
You can also search around, and review archived threads and posts on here too.
Tight lines.