According to the United States Census Bureau, the city has a total area of 2.6 square miles, all land. San Pablo lies on a sedimentary plain between the northern end of the Berkeley Hills and San Pablo Bay, although the city limits do not extend to the bayshore. The city is traversed by two principal creeks, Wildcat Creek and San Pablo Creek, both of which originate in the ranges to its southeast. The minor Rheem Creek also runs through the city. It is also traversed along its northeast limits by the Hayward Fault, a major branch of the San Andreas Fault which lies to the west.
Interstate 80 (Eastshore Freeway) passes through San Pablo. There are several communities to the north of the City and separated from the City, but which have San Pablo, California mailing addresses. These include the census areas of Tara Hills, Bayview, and Montalvin.
The area in which today’s San Pablo is situated was originally occupied by the Cuchiyun band of the Ohlone indigenous people. The area was claimed for the king of Spain in the late 18th century and was granted for grazing purposes to the Mission Dolores located in today’s San Francisco. Upon Mexico’s independence from Spain, church properties were secularized and in 1823, the area became part of a large grant to an ex-soldier stationed at the San Francisco Presidio, Francisco Maria Castro. The grant was given the name Rancho San Pablo, thus originating the name for today’s city as well as for one of the East Bay’s oldest principal roads, today’s San Pablo Avenue (called in the prior Spanish era “El Camino Real de la Contra Costa”).
A historic reproduction of the city’s Mexican era is designated as a California State Landmark (No.512): the Alvarado Adobe, originally constructed in 1842 by one of Francisco Castro’s sons, Jesus Maria Castro, for his mother, Gabriela Berryessa de Castro. Upon Gabriela’s death in 1851, it was inherited by her daughter, Martina Castro de Alvarado, wife of Juan Bautista Alvarado, who was Governor of California from 1836 to 1842. The Alvarado Adobe was demolished in the mid-20th century to make way for a motel. A reproduction was built later in the century which is located in the San Pablo Civic Center on the northwest corner of San Pablo Avenue and Church Lane. A single beam from the original structure is incorporated into the roof of the replacement structure, at the rear of the adobe facing the interior courtyard.
The first post office was established in 1854. The city incorporated in 1948. Since the middle of the 20th Century College Center at El Portal has been the backbone of the community’s retail economy. The city hosts the county’s western campus of the Contra Costa Community College District. This school is named Contra Costa College and is part of the California community colleges system.