The Natural Pier Bridge shows how engineers incorporated a natural feature into bridge design. Designed by Montana Highway Department bridge engineers, it is a standard riveted Warren through truss and is unusual because one of its piers is anchored to a rock outcrop in the Clark Fork River. The bridge was once part of the Yellowstone Trail, which traversed Montana from Lookout Pass to the South Dakota border in southeastern Montana. In response to pressure from lumber companies and the Yellowstone Trail Association, Mineral County began an ambitious bridge-building program in 1916. Although the county was responsible for construction, fiscal limitations and the bridge’s location near the Lolo National Forest led county commissioners to seek federal financial aid. In early 1917, the county contracted with the Missoula-based Lord Construction Company to build the bridge. Work progressed steadily for several months until the county ran out of money. After obtaining additional federal funds, the county commissioners called a referendum to raise money to complete construction, but the vote could not be held for several months because of the law. With the needed money eventually acquired, the bridge was completed in 1918 at a cost of $100,000.