You may or may not have noticed these little bronze markers on buildings, sidewalks, or in concrete monoliths in the countryside. These are the benchmarks that let surveyors know where they are. Their locations are accurate to around a part per billion in latitude, longitude, and altitude. This one, in particular, seems to be set through the sidewalk by the bridge (probably anchored to bedrock below) to let surveyors easily check the settling of the dam.
