The United States Census Bureau says that the city has a total area of 63.7 square miles (165.1 km²). 45.3 square miles (117.4 km²) of it is land and 18.4 square miles (47.7 km²) of it (28.90%) is water. The Hayward Fault Zone runs through Hayward. The United States Geologic Survey has said there will probably be a big earthquake on this fault zone. This earthquake will probably cause a lot of damage. Other cities next to Hayward are Union City, Fremont and Pleasanton.