The station is in the top of the concrete abutment on the northwest corner of the bridge, quite easy to spot. It is marked simply "Bureau of Reclamation Triangulation Station", with no numbers or date. It appears in neither the NGS nor the Geocaching database.
The bridge was built in 1941, so the station could be of any age post 1941. Other than people having hammered on it, likely with rocks (I wonder why people would do that), the station is in good condition. It's a standard brass disc, set into the concrete of the abutment.
This bridge is the last one which crosses the Kettle River before it empties into Lake Roosevelt, which is actually the reservoir formed in the Columbia River by the Grand Coulee Dam, also completed in 1941.