Downtown San Jose built on filled tidal marsh and bay mud

Much of downtown San Jose, including the area around San Jose City Hall, was originally tidal marsh and bay mud at the head of the Guadalupe/Alviso slough system and was filled during the 19th and early 20th centuries to create developable land. The underlying bay-mud and artificial fill produce high liquefaction and subsidence susceptibility during strong earthquakes, a documented geotechnical characteristic that affects foundation design and emergency planning. The Guadalupe River was channelized through downtown in the 20th century to control flooding of this low-lying, reclaimed landscape, altering tidal influence and floodplain dynamics.