San Diego is situated along the Pacific coast near the U.S.–Mexico border, forming a key part of the transborder San Diego–Tijuana region. San Diego Bay, described by SDSU professor Monte Marshall as “the surface expression of a north-south-trending, nested graben,” anchors the city’s coastal geography. The Rose Canyon and Point Loma fault zones are connected to the San Andreas Fault system, reflecting the area’s dynamic geological activity. About 40 miles east, the Laguna Mountains rise within the Peninsular Ranges, part of the broader American Cordillera.

The city itself is defined by roughly 200 deep canyons and hills separating its mesas. These natural features create scattered pockets of open space, contributing to San Diego’s low-density, car-oriented urban layout. Residents traditionally build on the mesas, leaving canyons largely wild, which gives the city a segmented feel with natural separations between neighborhoods. The San Diego River runs east to west through the city, creating a central valley that divides northern and southern sections, while reservoirs and parks like Mission Trails Regional Park provide additional natural barriers and recreational areas.

Notable peaks within the city include Cowles Mountain (1,591 ft / 485 m), Black Mountain (1,558 ft / 475 m), and Mount Soledad (824 ft / 251 m). Beyond city limits, the Cuyamaca and Laguna Mountains rise to the east, leading eventually to desert regions, while the Cleveland National Forest lies just a short drive from downtown. Fertile valleys northeast and southeast of the city support farming and agriculture, complementing the urban and natural landscapes that define San Diego.