San Diego's southernmost beach lies within Border Field State Park, an area with sand dunes and salt marshes favored by horseback riders and hikers. The Tijuana River Estuary, designated as a Wetland of National Importance, is a haven for endangered birds. The beach has soft sand, but due to the amount of debris and seaweed that washes up on the shore, it's not a particularly good place for sunbathing. You're better off going for a long walk or picnicking at one of the Monument Mesa sites, which offer scenic ocean views, barbecue grills, and shaded areas. Flooding in winter often restricts access, but normally the park is open to pedestrians, hikers, and equestrians on weekdays. Because of state budget cuts, motorized vehicles are permitted only on weekends and holidays. Beware: Swimming and wading are discouraged due to inshore holes and rip currents, and because no lifeguards are on duty. After heavy rains, runoff from the Tijuana River and nearby ranches can pollute the water, leading to occasional beach closures. Bring snacks and drinking water because the closest place to buy food is 5 miles away in Imperial Beach. Amenities: parking (fee), toilets. Best for: solitude, walking.