Yellow Creek Bridge (Bridge No. 20-0021) and Arroyo Seco Bridge (Bridge No. 20-0023) are located on SR 121 at Post Miles (PM) 6.52 and 8.43, respectively, in Sonoma County, California (Figures 1-1 and 1-2). Yellow Creek Bridge is located approximately 0.2 mile south of the intersection of SR 121 at the intersection of SR 116 and Bonneau Road. Arroyo Seco Bridge is located approximately 1.6 mile east of the intersection of SR 121 at SR 116 and Bonneau Road.