Depending where you are in Portland, the most convenient GA field may be across the river in Vancouver WA. Historic Pearson Field (KVUO) is the closest airport to downtown Puddletown. That's where I was based for 21 years until moving to AZ earlier this year.
Pearson's runway is 3200'x60' so your training won't be spoiled by excessive pavement. It's uncontrolled, but because of its proximity to KPDX there is an unusual -- but very easy -- ATC communication requirement. The lone FBO on the field, Aero Maintenance (360-735-9441) has a fleet of ... um, experienced ... C-150s and 172s. They won't win any beauty titles, but they're well maintained. Tell Clu at the front desk I sent you.
Lots of interesting aviation history at Pearson, going back to 1905. Go on a Saturday and visit the Education Center; see the Chkalov Memorial, and wander around Officers Row and the replica of Fort Vancouver.