M-Dan!
If you're tight on time and travel and obviously may not have to chance to "cook and eat your catch", (because you don't want to, out of the Willamette anyway!), I'd seriously just fish in and around downtown Portland!
There's several access points, along the sea wall, down on the waterfront of the Willamette River, right in downtown.
Or, drive towards "Lake Oswego", (Well marked signs, from downtown leading towards the town of Lake Oswego) and simply "fish wherever you see river access" along the way.
I mention this choice, after talking to the owner of River City Fly Shop, in Tigard, this past week and he was telling me about the 12" to 16" Smallies he and friends have been catching on flies, as he put it............ "Anywhere we could get a streamer into the Willamette River, from right downtown Portland, all the way out to Lake Oswego!".
Just a thought if you wish something close, easy and perhaps a lot of fun!?!
Good luck and have a great time!