Border Field State Park stands at the southernmost point in California, where the Pacific coast meets the international boundary between the United States and Mexico beside Playas de Tijuana. The park includes beach, dunes, wetlands, and the southern part of the Tijuana River National Estuarine Research Reserve. Its historical importance stems from the Treaty of Guadalupe Hidalgo, after which the joint survey establishing the modern border began here in 1848; Friendship Park and the Initial Point of Boundary lie just inland. The area later served as the base for Border Naval Outlying Landing Field during World War II and remains significant as habitat for migratory and resident birds.