Hello Modocdan, well just head up the gorge and when you cross the Sandy, take the offramp and you can start following the river upstream. You could try google maps and in 'get directions' plug in portland or to troutdale or to get you close, then right past the troutdale exit you'll see a river entering the Columbia...click on 'satellite' and have a closer look.
Cheers,
MontanaMoose
Edit: This is for everyone...
The feature mentioned above
can put you on the sidewalk at
that 'old house' you used to live
in when you were a kid. Yesterday
was showing the wife and could get
a view of the front door of the house
I lived in about 50 years ago.