 At the time, its graceful arch was the longest single-span reinforced concrete bridge in the world or perhaps just in the West and has been listed on the Washington State and National Historic Register since 1976.Until 1972, when the Washington State Department of Transportation re-routed Highway 20 (then known as Star Route 20) outside the town, the Thompson Bridge was the only connecting thoroughfare across the Baker River and into eastern Skagit County.The bridge was originally designed by Bowerman and McCloy Consulting Engineers of Seattle, and built by J.R. Wood Contractors also of Seattle.