There is some smoke coming from the peat on the north side of the island, but no more open flames, and no homes are threatened, Boyer said.
The fire started late Thursday or early Friday, but since the island is not in the jurisdiction of any fire department, residents were left to fight the blaze on their own.
Boyer estimated that between 550 and 600 acres of the 2,000-acre island had burned. He did not have information about how many homes had been damaged or destroyed.
Emergency crews have made regular trips to the island, which can only be accessed by boat, to make sure no lives were in danger, but other than that they don't have the resources to fight a fire like this one, Boyer said.
The fire has been burning peat, or partially decomposed vegetation, both above ground and underground, Boyer said. Peat fires can be expensive and dangerous to fight.
The American Red Cross has also visited the island to offer assistance to anyone wishing to voluntarily evacuate, said Jim Mallory, public information officer for the Contra Costa County area Red Cross.
Mallory said the Red Cross helped three people whose house has been severely damaged by the fire.
Boyer said the remaining residents, about 20 people, continue to refuse assistance.