Champoeg State Heritage Area - state parks website

I haven't been yet. Sounds like it has nice paved bike/multi-use trails (some sources say 4 miles of paved trail). Several sources (such as this Portland Family Adventures article) say the trails can be a bit cracked and bumpy with tree roots.

South of Portland and Wilsonville. "Off US 99W, 7 miles E of Newberg. From I-5, take Exit 278 and head west. Follow the signs."