The cache is NOT at the posted coordinates.
Visiting all the murals depicted on this map is a great way to see The Dalles.
To find the true coordinates for this bonus cache, you will need to gather clues while visiting the "WALLDOGS DO THE DALLES" Adventure Lab.
https://adventurelab.page.link/7h5m
The BONUS cache may be found at:
N 45° A W 121° B