The Bridge Street Bridge Seismic Upgrade augmented the 1900’s historic structure to meet seismic safety requirements. The bridge spans the Arroyo Grande Creek. The north span is a truss structure extending the entire creek width, and the south span is a steel girder structure spanning a short flood plain area. Concrete abutments support the bridge at each end, and an offset pier on the south bank supports the connection between the two spans. The augmentation entailed construction of structural facing and encasing the bridge abutments and the offset pier in structural elements designed to accommodate seismic forces. New foundations were constructed to support the weight of the new structural elements and to resist the lateral seismic loads of the entire bridge structure. For this project, Earth Systems performed a soils engineering investigation involving site reconnaissance, field exploration, laboratory analysis of samples, geotechnical engineering analysis. The Earth Systems team developed recommendations for the schematic design of foundations, and these recommendations complied with Caltrans design practices as they apply to seismic upgrades of historic bridges.