Head north out of Portland, cross the bridge over the Willamette Channel and arrive on Sauvie Island. Head north through farmland and eventually you'll arrive at a gravel/dirt road. Follow the dirt road and you'll see signs for Clothing Optional beaches. Head west on a compacted dirt road and you'll pass this body of water before arriving at yet another along with a boat ramp.
All in all you'll have a grand adventure. Retrace your "footsteps" and you'll be able to stop and purchase your choice of any kind of berry imaginable.