Truck-size shipping container washes up on S.F. beach

Baker Beach was covered in debris after a shipping container washed ashore on Sunday, Dec. 13, 2015. Baker Beach was covered in debris after a shipping container washed ashore on Sunday, Dec. 13, 2015. Photo: Drew Laughlin, Special To SFGATE Photo: Drew Laughlin, Special To SFGATE Image 1 of / 9 Caption Close Truck-size shipping container washes up on S.F. beach 1 / 9 Back to Gallery

U.S. Coast Guard officials are warning mariners to be cautious as they navigate the waters off San Francisco Bay after a cargo ship lost a dozen large containers just outside the Golden Gate Bridge Friday evening in heavy seas.

One of the containers, which was filled with plastic pallets, broke apart on the rocks near Baker Beach over the weekend and crews were still working to clean up the mess as of Monday.

The Manoa, an 810-foot cargo ship operated by Matson Navigation Co., was leaving the Port of Oakland en route to Seattle Friday evening when it encountered 19-foot waves and 20 mph winds just outside the Golden Gate Bridge, which caused 12 containers to slide off the ship, Coast Guard officials said.

Most of the containers were empty, but a few were loaded with various kinds of packing material, the Coast Guard said. None of the materials inside the containers are hazardous to marine life, officials said, but the owner of the ship hired an environmental contractor to track down the containers and clean up any debris that washes ashore.

Some of that debris was already evident by Sunday morning as Salesforce CEO Marc Benioff tweeted a picture of one of the containers resting on the rocks between Baker and China beaches in San Francisco.

Arthur Fraser, 68, went down to the beach on Sunday and was taken aback by what he saw as the beach was covered in pallets spilled from the washed up container.

“I was horrified to see the beach strewn with these green plastic pallets,” he said. “There were just so many. Not hundreds, but thousands.”

While Fraser said the initial sight was depressing, his hopes were quickly buoyed when he encountered a group of high-school age boys who were diligently running into the surf to collect the debris and stacking the pallets on the beach, out of reach of the high surf.

He said he worked with the boys for a few hours as they scoured the waves for floating debris.

“The surf was just full of the them,” he said.

The Coast Guard and National Oceanic and Atmospheric Administration were working with the state and city officials to clean up the contents of that container Monday morning, collecting the pallets using rakes to get the smaller pieces of debris and using metal saws to slice up large pieces of the container, which were washing up from the headlands to the west.

Officials issued a warning to other vessels cruising the waters around San Francisco to be on the lookout for the other 11 containers, which may have sunk but have yet to be located.

The parking lots at Baker Beach were closed to the public Monday to give access to clean up crews, said Adrienne Freeman, a spokeswoman for the National Park Service, but beach-goers on foot could still use the beach so long as they gave room to the clean up crews.

Officials asked members of the public to contact the Coast Guard Sector San Francisco Command Center at (415) 399-7300 if they spot any of the missing containers.

Kale Williams is a San Francisco Chronicle staff writer. E-mail: kwilliams@sfchronicle.com Twitter: @sfkale