With the collapse of its famous namesake on Dec. 21, the Bird Rock community is left without a physical icon. This incident, however, is only the latest in a long history of collapsing and eroding rock formations, guaranteeing that the view of the coastline is a fleeting one. Philomène Offen, curator of the Bird Rock History Museum at Bird Rock Coffee Roasters, discovered a dramatically changing coastline in old photos when she began documenting the history of the community a year ago. “Obviously, the coastline is always changing,” Offen wrote in an e-mail. “When I was doing my Bird Rock history project in 2009, I noticed a number of other rocks — not as big as Bird Rock, but substantial nonetheless — that appeared in 1920s-era photos but are now long gone.” Carol Olten, historian for the La Jolla Historical Society, said historical images of La Jolla’s coastline bear witness to the shifting geology. Going as far back as the early 1900s, the historical society’s collection documents the various and inevitable disappearances of rocky landmarks. The earliest shows “Cathedral Rock,” a sandstone La Jolla arch that eroded and collapsed into a pile of rocks in 1906. Eventually, even the fragments of the once-popular formation disappeared. Another example is the “alligator head” formation at La Jolla Cove, which featured an arch that formed the “body” of the beast, which people could walk over to reach the snout. A storm in the late 1970s caused the arch to collapse, severing the head from its body and forever disfiguring the rocky reptile. Though what is seen when looking out at the shoreline will inevitably change over time, La Jolla is unique in that those changes take place more slowly than almost anywhere else along the California coast. According to Mike Hart, a private geological consultant, two formations create La Jolla’s coastline: the Cabrillo Formation and the Point Loma Formation. The exposed sea cliffs created by these formations are made up of hard, well-cemented sandstone interbedded with clay shale, which Hart said makes them highly resistant to erosion. Furthermore, the cliffs and rock formations in La Jolla are some of the oldest rocks on the coast, dating back to the Cretaceous Period, more than 65 million years ago. The older the rock, the harder and more resistant it is to erosion, which is why the relatively young rock on Mount Soledad makes the region so much more susceptible to landslides, Hart said. “You walk down to the beach and you look at [the rock] and you think, ‘How can that stuff erode?’” said Hart. “It’s a calcium carbonate, and it’s not highly soluble. It cements the grains together, but eventually, of course, it will give way to constant abrasion.” Erosion occurs as a result of waves getting into fractures in the rock, undermining areas of the structure. Eventually, the weight is too much to support and parts of the rock will crumble. Hart said geologists call a case like the one in Bird Rock “episodic.” “You can go for a hundred years and not notice a difference in the formation,” he said. “But suddenly a cave will reach its critical point. It will reach its maximum ability to overarch an area and it collapses.” That is what happened to Bird Rock’s beloved landmark. For a few years, the size of the hole in the arch had been getting bigger and bigger, and some residents were not surprised by the eventual collapse. Don Schmidt, a member of the La Jolla Historical Society and 15-year resident of Bird Rock, predicted that the rock would crumble soon. “It was getting thinner and thinner, and it was just a matter of time,” Schmidt said. “But when I found out this rock was 70 million years old, I thought, ‘What are the chances in my short little lifetime that I would see something like that happen?’” Schmidt, who says he named his dog after the rock because of their similar shapes, believes the legacy of the rock will live on in the stories passed down to future generations. “I think it will be part of the Bird Rock lore for years,” he said. “Years from now, people will tell about the day ‘Bird Rock’ broke. Perhaps people will think about it on a personal level, that nothing is forever, even a solid rock like that. I think it will enrich the community on some level.” Though it may be the tragic end of an era for members of the Bird Rock community, the rate of change along the coastline is something to be grateful for, Hart said. “If we had the rock along the coast that Mount Soledad has, we’d see a lot faster erosion, Hart said. “We’re fortunate we have some of the hardest sedimentary rock in California along our coastline.” But for now, as Offen said, the birds will have to find another rock.