A mysterious park I found on my third try.  On a square of black asphalt behind a black, chain-link fence signed Lake Oswego Skatepark, there are some wooden ramps topped with sheet metal.  The location is permanent, but the park is seasonal.  It opens Friday, July 14th and will close sometime in the fall.
 

Skatepark Hours
  Monday - Saturday      10am to 8pm
  Sunday                       12 to 8 pm
 

Fees
  Day Use            $3
  Summer Passes
    Residents       $10
    Nonresidents  $15
 

Location
  Plinkington St. (Rd?).   Just north of Jean Rd (5700 block) and south of Lower Boones Ferry Rd.  East of 1-5 and Nature's.
 

Directions
  From I-5 take the Lake Oswego / Durham exit #290 and head east on Lower Boones Ferry Road.  Go about 3 lights and then at Plinkington, go right (south).  Look to your right for the black fence.  If you reach the four way stop intersection of Jean and Plinkington, you have gone too far.