Erosion of a bluff that sent debris falling to the beach near downtown Del Mar has caused officials to close off a 30-yard-long area at the top of the site.
Lt. John Schooler of the city's lifeguard crew said Wednesday that the incident occurred about 6 p.m. Tuesday and was witnessed by several beach-goers.
"There was a rumble and a loud thump as the dirt and debris hit the sand," he said. "But no one was injured and no homes were threatened."
The avalanche of unstable sandstone occurred within a short distance of the Santa Fe Railway tracks that run along the North County coast. Railroad officials were alerted to the incident, but trains continued to run Wednesday, Schooler said.
"Bluff failure is not uncommon along the coastal cliffs, but this was a rather large section," he said. "So we barricaded off a section above and one below on the beach in case any rocks continued to fall. That way they won't hit anybody."
Officials said the fallen section was about 60 feet high and was located near the foot of 9th Street downtown.
The erosion was believed to have been caused by rains that wet and then dried out the unstable sandstone. "It can happen any time of the year," Schooler said. "Eventually, the fallen material will become part of the beach.
"This is actually one of the ways we get sand on the beaches here," he said. "But it's also important to let people know to use caution around these unstable areas. You wouldn't want to be standing on top of a bluff when something like this occurs."
Mike Martin, a spokesman for the Santa Fe Railway in San Bernardino, said officials are aware of the failing bluffs. "Our tracks have been running along those for 100 years," he said. "Our people are aware of the danger of erosion."
Martin said the railroad has added reinforcement along coastlines to guard against wear and tear.
The area will be cordoned off for several days as a safety precaution, officials said.