During the first half of the 20th century, the city of San Francisco relocated its cemeteries to Colma, California, leaving the city with a surplus of old tombstones. Many of these tombstones were used as building material in the growing city, including as breakwaters in the Marina District, as path liners at Buena Vista Park, and at Aquatic Park, where they can still be seen at low tide. A cache of tombstones was also used to build the Wave Organ near the St. Francis Yacht Club. Today, there are only three cemeteries remaining in San Francisco: Mission Dolores, the Presidio, and the Richmond District Columbarium.