Portland, OR

Portland Metro
  “Metro serves more than 1.5 million people in Clackamas, Multnomah, and Washington counties. The agency’s boundary encompasses Portland, Oregon and 24 other cities – from the Columbia River in the north to the bend of the Willamette River near Wilsonville, and from the foothills of the Coast Range near Forest Grove to the banks of the Sandy River at Troutdale.”  Phone  503-665-4995 ext. 0  Here is the website for Metro’s Parks and Venues.
  Wheelchairtraveling.com on Portland’s accessibility
Access Recreation, conceived and led by Georgena Moran, is a wonderful project which provides assessments and videos to benefit hikers with disabilities in the Portland Metro region.  There are candid descriptions, photos, maps and annotated profiles.    Access Trails  Overall map   Hiking trails videos.
     
Wheelchair AccessibleCooper Mountain Nature Park   has a 3/4 mile accessible loop trail      Trail Map  Field Guide
Wheelchair AccessibleScouters Mountain Nature Park has a 1/4 mile accessible loop at the top of the hill.  Field Guide  Map
Wheelchair AccessibleSmith and Bybee Wetlands Natural Area Field  Guide   phone 503-797-1545  Map
The Interlakes Trail and the 40-mile Loop Trail are both wheelchair accessible as are the wildlife viewing platforms and restroom.
Wheelchair AccessibleMount Talbert Nature Park  Website  phone North Clackamas Parks and Recreation District at 503-794-8041 Trail Map  There is a “short gravel trail” and picnic shelter which are accessible.
Wheelchair AccessibleGraham Oaks Nature Park   Field Guide
“Much of the park is wheelchair accessible, although some trails are more challenging. ”  I suggest you call first for clarification: 503-665-4995
Wheelchair AccessibleForest Park      Map of Trails and Roads Described on wheelchairtraveling.com
Leif Erikson Drive is an 11 mile gravel road.
The Lower Macleay Trail is paved for a short distance ending at Balch Creek.
Wheelchair AccessibleBlue Lake Regional Park  Map     The 2 mile Blue Lake Loop Hike described by OregonHikers.org