 The Tijuana River is an intermittent river, long, on the Pacific coast of northern Baja California in Mexico and Southern California in the United States.It drains an arid area along the California–Baja California border, flowing through Mexico for most of its course and then crossing the border for the last of its course where it forms an estuary that empties into the ocean.The river's lower reaches harbor the last undeveloped coastal wetlands in San Diego County, and some of the last in Southern California, amidst a highly urbanized environment at the southern city limits of Imperial Beach.