"Look closely as you wander the winding, tree-lined paths. Here, in the city’s earliest park, you’ll also find traces of some of San Francisco’s earliest tombstones. Following the mass relocation of the city’s cemeteries to Colma in the first half of the 20th century, San Francisco was left with acres of new, buildable property, and a surplus of old tombstones. Only the tombstones and mausoleums of the city’s rich, famous, and those with living families who paid to have markers moved were relocated. The rest of were sent to the rubble pile, eventually becoming building material in the growing city. The huge numbers of unclaimed tombstones ended up being used in breakwaters in the Marina District, as path liners at Buena Vista Park, and at Aquatic Park, where the distinctive stones can still be made out at low tide. More recently, a cache of old stones was used to build the wonderful Wave Organ near the St. Francis Yacht Club. Today, only three cemeteries remain in the city of San Francisco—at Mission Dolores, the Presidio, and the lovely Richmond District Columbarium." - ATLAS_OBSCURA
