Meanwhile, Coast Guard officials defended the response to the spill -- even after their initial reports Wednesday indicated that only about 150 gallons of fuel had been spilled.
Wildlife authorities also combed area beaches, mostly on a hard-hit swath between Richmond and the mouth of the Bay, to rescue as many as 100 oil-soaked waterfowl.
Tides carried a plume of heavy fuel beneath the Golden Gate Bridge and into the Pacific Ocean.
Officials had cleaned up at least 9,500 gallons of the marine bunker oil Thursday, in the wake of their delay in revealing to the public the severity of the release.
Cleanup crews deployed 1,800 feet of floating oil-absorbing booms to contain the oil and protect environmentally sensitive or public areas.
Coast Guard officials said they knew within an hour Wednesday that the original report was too small, but they could not get a full handle on the size of the spill until late afternoon.
Still, they waited at least five hours to divulge that 58,000 gallons had spilled.
Environmentalists and San Francisco officials berated the agency for not providing timely information and promised to examine what happened.
San Francisco Mayor Gavin Newsom said the city was considering filing a lawsuit against the shipping company and perhaps federal agencies.
"We would have responded differently if we had accurate information from the get-go," Newsom spokesman Nathan Ballard told the Associated Press. City workers, for instance, would have initially laid more boom lines to contain the oil, he said.
Gov. Arnold Schwarzenegger is expected to visit the spill command center at Fort Mason today for a briefing, and state Sen. Carole Migden, D-San Francisco, announced that a Senate committee would hold a hearing Nov. 19 in San Francisco into the causes and response of the spill.
"We take this spill very seriously, and we will do everything we can to protect and preserve the beauty of California's landmark estuary," Schwarzenegger said Thursday.
The Coast Guard also was unprepared to explain the whereabouts of John Cota, pilot of the Cosco Busan.
He had left the container ship before official investigators arrived. At first, Coast Guard officials told reporters Thursday they were not able to take drug and alcohol samples from Cota or interview him until he appeared at their request Thursday morning, 26 hours after the incident.
They later clarified such tests were performed within a few hours and that the alcohol test results were negative. Drug test results will not be available for days.
By Thursday evening, ribbons of oil were reported as far south as Hunters Point, east to Oakland, up through Raccoon Straits to Richmond, along the San Francisco waterfront, several miles outside the Golden Gate Bridge, from south of San Francisco's Ocean Beach to Marin County's Stinson Beach in the north.
Marin beaches just north of the Golden Gate appeared to experience the thickest concentration of oil.
"We mobilized as if it was a big spill right away," said U.S. Coast Guard Capt. William Uberti, in spite of an initial estimate provided by the captain of the Cosco Busan that the vessel was only missing 140 gallons of bunker fuel oil.
The ship hit the Bay Bridge about 8:30 a.m. Wednesday, doing no damage to the concrete abutment but mangling its plastic bumper. The incident left a horizontal gash near the front of the ship, measuring 100 feet long, 12 feet wide and 3 feet deep.
Two of the ship's fuel tanks ruptured, and most of the fuel poured out in 20 to 30 minutes, Uberti said.
The cleanup effort was hampered by bad weather -- a fog that limited authorities' attempts to assess the spill, and tides that alternately pulled the oil toward the ocean and pushed it farther into the Bay.
About 200 people from at least 13 federal, state and local maritime, environmental and safety agencies worked on land and water Thursday, and 100 more were to join the effort today, said Barry McFarland, incident commander for the O'Brien's Group, a Brea-based disaster management firm hired to deal with the incident.
While oil sightings came in Wednesday from various locations along San Francisco's waterfront, it was not until Thursday morning, when fog lifted and authorities were able to see the oil from the air, that the extent of the contamination could be gauged.
The U.S. Coast Guard deployed 10 vessels equipped with cleanup gear, seven inside the Bay and three in the Pacific. Their ability to pick up the drifting oil was limited by the thin concentration in most areas, which make skimming difficult, said Coast Guard spokeswoman Mariana O'Leary.
Most of the 8,000 gallons of oil picked up Wednesday and 1,500 gallons collected Thursday by skimmers and stored in tube-shaped bladders towed behind Coast Guard cutters and other contracted ships was collected where the oil was thickest. That heavy concentration covered an area from Raccoon Strait, between Tiburon and Angel Island, to Brooks Island, just off Richmond.
Meanwhile, journalists and officials dealing with the spill also had to sort through who, exactly, might be responsible for the spill.
Darrell Wilson, an Oklahoma-based public relations specialist, showed up at the waterside command center announcing that the ship's owner, Hong Kong-based Regal Stone Ltd., had hired him to speak for them.
He expressed regret on behalf of the firm as well as relief that no one had been injured, and he said the ship had been leased by South Korean Hanjin Shipping.
A representative of Hanjin, however, said in a phone call from South Korea that her firm had chartered the vessel from Synergy Maritime, a Cyprus-based firm that employs its crew. She declined to make a formal statement, other than to disavow earlier reports that Hanjin owned the vessel.
The environmental impact of the spill continued to spread Thursday.
Tar balls the size of golf balls had been spotted in the water outside the Golden Gate, with smaller tar balls spotted in the Bay.
The state Department of Fish and Game reported that 26 live oil-covered birds had been recovered and at least six had been found dead. The count of dead birds could easily reach into the hundreds in the coming days, wildlife experts said.
There are no reports yet of mammals suffering from affects of the spill, according to the Marine Mammal Center, whose offices are at Rodeo Beach in the Marin Headlands.
Although the spill is not very large, it is still a "lot of oil for San Francisco, for California. This is a very environmentally sensitive area, so that's of great concern," Uberti said.
Sejal Choksi, a spokeswoman for Baykeeper, a group that fights water pollution in the Bay, said it did not appear that the Coast Guard moved as quickly as it could have.
"The Coast Guard doesn't seem to have boomed it off immediately enough because the spread of the oil has been great," she said.
"It is really tragic. I'm not sure how it is going to get adequately cleaned up. We are going to see the impacts for quite some time."
At Rodeo Beach, 10 contaminated birds were found, seven of which were still alive. The birds are being taken to the International Bird Rescue Research Center in Cordelia, where they will be washed with a grease-cutting detergent.
The cleanup effort at Rodeo Beach began about noon Thursday, where a half-dozen workers wearing protective clothing and gloves shoveled up globs from the oil spill as students on nature tour groups looked on. A part of the beach tideline is marked by black, gooey oil, and workers are trying to finish the cleanup before the tides move back in.
The cleanup is being conducted by contractors hired by the company that owns the vessel that caused the spill, but Coast Guard and state officials are monitoring the cleanup procedures. The company has deployed oil skimmers -- boats that skim water and take out oil. Three are working outside the Golden Gate.
"So far, they are doing a very good job," Uberti said.
Terry Picon was walking her dog Thursday at Crissy Field, a regular haunt for her and her black standard poodle JB.
"I was just out there yesterday, looking at the sea lions and saying what a beautiful place," she said. "Then I heard on the news about the oil spill. It's awful. You don't expect it to happen in your own backyard. Sure sounds like somebody was asleep at the wheel."
For years, biologists have been concerned that a significant oil spill inside San Francisco Bay could cause major environmental damage. The reason? The Bay has only one narrow opening at the Golden Gate, and the right combination of currents could push oil south, coating sensitive San Mateo, Alameda and Santa Clara counties' marshes, which are home to fish, birds and harbor seals.
On Wednesday, signs were posted warning the public not to swim or fish in several areas, and a hot line was set up to take reports of fouled wildlife.
U.S. Coast Guard Petty Officer 3rd Class Michael Anderson said the agency came up with the preliminary estimates by taking water samples from the Bay and comparing the liquid load on the vessel before and after the crash.
"It's a fairly complicated process," he said.
The last spill of this magnitude happened in 1996, when the Cape Mohican, a military reserve vessel, spilled 40,000 gallons of fuel oil into the Bay near Pier 70.
Before that, an explosion on another ship, the Puerto Rican, spilled 1.5 million gallons of oil in the open ocean off the Golden Gate in 1984.
By comparison, the Exxon Valdez spill was 11 million gallons.
The incident had no effect on the bridge or anyone driving across it, and Caltrans engineers who examined the structure determined that the vessel did not make contact with the actual concrete abutment, said Caltrans Bay Bridge spokesman Bart Ney.
But the impact damaged the vessel, which was carrying containers for the China Ocean Shipping Co.
Once the ship's crew and the Coast Guard had transferred fuel from the breached tank and contained the spill with absorbent foam barriers, it was moved across the Bay to Anchorage Nine, offshore from the former naval station in Alameda.
The Coast Guard prohibited boats from getting within 100 feet of the ship.
The San Francisco Public Health Department issued a statement noting that oil vapors had sickened people onshore, causing headaches and nausea but said the fumes posed no long-term health effects.
Ney said the damage to the bridge could be fixed without too much trouble, but it probably would require an emergency contract.
Coast Guard officials canceled the swimming portions of two triathlons scheduled for the weekend.
Staff writers William Brand, Mark Gomez and Leslie Griffy and the Associated Press contributed to this story.