Two identical single-spanned concrete tied arches were constructed by the Colonial Building Company in 1924 over the North Hamma Hamma and the South Hamma Hamma River. Spaced a few hundred feet apart, their arched forms frame a pathway of trees creating the momentary illusion of a serene, sheltered boulevard along Highway 101 on the Olympic Peninsula. Each bridge is 154 feet long, and consists of a 150 foot three hinged arch with a rise of 30 feet. Unlike the flat truss or girder, the arch exerts a horizontal thrust on the skewbacks. In most arches, massive abutments and foundations are necessary to resist the horizontal thrust. However, in the tied arch, the horizontal thrust is resisted by longitudinal ties which extend between the hinged springing points. In the Hamma Hamma River Bridges, the deck slab itself, which is hung by suspenders from the pair of arch ribs, acts as a tie. Since the arch is in compression, the deck slat, is subject to a tensile stress. The double function of the deck slab was an economical solution, and it eliminated the need of massive abutments. Originally, six reinforced concrete struts connected the Hamma Hamma River arches above the roadway. However, two struts were removed from each bridge to increase the vertical clearance of the spans. The North and South Hamma Hanuna River Bridges are two of five concrete tied arches within the State. Of the five bridges, their arch spans are the longest. They are a rare concrete arch form.