State Route 123 in Northern California, named San Pablo Avenue for virtually its entire length, is a major north-south state highway along the flats of the urban East Bay in the U.S. state of California. Route 123 runs a relatively short 7.39 miles (11.9 km) between Interstate 580 in the south and Interstate 80 in the north. San Pablo Avenue itself, a portion of Historic US 40, continues well past these termini but without the Route 123 designation.