Border Field State Park 1500 Monument Rd, San Diego, CA92154 Border Field State Park is considered a part of the Tijuana National Estuarine Research Reserve, one of 27 estuarine…More research reserves in the country designated by the National Oceanic and Atmospheric Administration. The park runs to the border where it meets Friendship Park and Monument Mesa, an international boundary marker placed here in 1851 to signal the start of the U.S. - Mexico border. Directly across the border is the Playas de Tijuana Bull Ring. Road access has been obstructed by state financial issues and other issues for the last two years, but bike and walking trails are still available. To access Border Field State Park, take Hollister Street until it ends and make a right at Monument Road.