From what I have found there are only three exposed timber truss vehicular structures remaining in Oregon.
Mott Bridge - http://www.bridgehunter.com/or/douglas/mott/
Middle Fork Willamette River Bridge - http://www.bridgehunter.com/or/lane/61805000001742/
Cascadia Park Bridge - http://www.bridgehunter.com/or/linn/17350016F04141/
I am always on the lookout for these rare timber structures, but like you said they are disappearing at an alarming rate.
Michael, great find here. Timber bridges are getting pretty rare in the West and this one is interesting.