Fire investigators have ruled out the possibility that the blaze, which erupted around 9 p.m. Sunday and burned until Tuesday afternoon, ignited naturally, Marin County fire Battalion Chief Mike Giannini said.
"A person was involved in what caused the fire," Giannini said.
Investigators have ruled out scenarios such a power line falling or an electrical malfunction as possible causes, according to Giannini.
"We've got it down to some level of human involvement being the cause of the fire," Giannini said.
Angel Island State Park Superintendent Dave Matthews said Wednesday the fire started in a camping area but investigators have not determined whether the blaze was sparked by a campfire.
Power was restored to the island at about 4 p.m. Wednesday, but the island remains closed to the public, Giannini said.
Angel Island is expected to reopen to the public on a limited basis Monday, Giannini said.
Additional information on the park is available by calling (415) 435-5390.
ABC7's Alan Wang wrote a back story about Angel Island and how he gained new respect for it.
Click here to read Alan's blog: The historical significance of Angel Island