Charles Nicholson, a hazardous materials specialist for Contra County Health Services, said he saw the flares on his way to work as he drove through the Willow Pass Grade of Highway 4 around 6:05 a.m.
"It looked very spectacular," Nicholson said. "The three flares were very visible."
The problem that caused the flares occurred at 5:53 a.m. and sent flames into the air for about 30 minutes.
Tesoro spokesman Mike Marcy said a gas-processing unit that takes excess gases and puts them back into the refining process came under too much pressure, and the gas was rerouted to a flare to relieve the pressure.
"We apologize for any undue concerns caused to the community," he said, adding that the flaring system worked appropriately and did not cause any danger to Tesoro employees or the neighboring community.
Nicholson said there was no indication the flaring caused any harm.
He said he contacted Tesoro around 6:15 a.m., when he got to his office, and Tesoro put out an official notification on the community warning system at 6:28 a.m.
Nicholson said the notification was a "little tardy," but said the refinery did what it needed to do make sure its facility was operating properly.
Marcy said the refinery waited to make the notification until it determined the visibility of the flares could cause some community concern, prompting the refinery to issue a "level one" notification on the community's warning system.
The refinery will investigate its equipment and procedures to figure out how to prevent similar situations in the future, Marcy said.
Nicholson said officials from the California Accidental Release Prevention Program will likely look into the malfunction, but that the refinery is not facing any penalties or fines.
"It's not terribly unusual, but it's not that frequent either," Nicholson said of the flares.