Governor Jerry Brown has declared state of emergency in southern California after a pipeline leaked tens of thousands of gallons of crude oil near Santa Barbara.
Officials said the pipeline was running at full-capacity when it broke on May 20.
While it has now been switched off, it is unclear how long the clean up will take.
Earlier estimates said a single slick had formed, stretching only four miles.
Emergency workers have been fanning out across Refugio State Beach to remove oil that is stuck to sand and rocks.
It is estimated about 21,000 gallons of oil have reached the ocean.
California Governor Jerry Brown declared the state of emergency on May 21 to help the state “quickly mobilize all available resources”.
Darren Palmer, an official with Plains All American Pipeline LP, who owns the pipe, said it was running at a rate of about 84,000 gallons an hour when it broke.
The pipe was built in 1991 and had been tested a few weeks ago, he said.
Darren Palmer said the company takes responsibility for the spill and will pay for the cleanup.
Environmentalists are concerned that the oil may harm wildlife including birds and whales.
The alarm was first raised on May 20 when authorities received reports of a foul smell near Refugio State Beach around midday.
Emergency responders found a half-mile slick in the ocean, Santa Barbara County Fire Captain Dave Zaniboni said.
They traced the oil to a ruptured onshore pipeline that was spewing oil into a rain water drain which ran to the ocean. The pipeline was shut off about three hours later.
The area has been closed to recreational and fishing activities. It is not clear if the area will be open for the coming Memorial Day weekend.