The cache is NOT at the posted coordinates.
To find this cache, you must complete all stages of the "Limerick Lab" adventure lab, which requires that you solve limerick puzzles at five locations in Wilsonville Memorial Park. The journal entries of the adventure lab stages provide you with the information you need to determine the final coordinates for this bonus.
Start the limerick lab by clicking here.
Bring your dogs, bring your kids, and bring your own pen.