I have seen this little bridge, it crosses an irrigation ditch and is readily visible from the road. It's maybe a mile or so east of Mancos on the lefft side of the highway.
Speaking of other bridges, there is a nice one just south of Durango on the line heading to farmington. It's below the 160/550 interchange. It's a nice big wooden trestle. If you continue up the hill on 160 towards Grandview you will see another small wooden tresle on the left- it's curved and on the really steep part of Bocea hill.