The fire "remained active" overnight, spreading farther north on Santa Rosa Island, part of Channel Islands National Park.
"Grasses on the island continue to be receptive to fire with the dry winds, low humidity, and warm days," read the incident overview from the National Park Service.
The island, often referred to as "California's Galapagos," is home to multiple rare plant species, including the iconic Torrey pines, which in the U.S. are found only on this island and in San Diego. On Monday, the fire swept through the Torrey pines grove on the island, and the extent of the damage remains unknown.
A drone is being brought to the island Tuesday to collect imagery of the trees.
"Upon initial assessments, fire crews are observing that the fire intensity was low and that the stand remains intact. When safe to do so, a fire effects crew will be assigned to make a full determination of condition and any long-term effect," the incident overview read on Monday.
The fire has burned 16,600 acres, which is over 30% of the island's 53,000 acres. The cause of the blaze remains under investigation, but fire started shortly after a stranded sailor set off a flare gun last Friday, according to the U.S. Coast Guard. The fire remains 0% contained.
Currently, 78 firefighting personnel have responded to the blaze along with an air tanker. More personnel, including a Hotshot crew, are expected to arrive on Tuesday. The fire has already destroyed two historic structures on the island, the Johnson's Lee Equipment Shed and the Wreck Line Camp Cabin, and it continues to advance across the largely uninhabited island.
As of Tuesday morning, the fire is within a half mile of the Water Canyon Campground, and crews are focusing on creating defensible space around the Vail and Vickers Ranch historic district, according to the incident overview.
"The firefighters that are working this fire are working extremely hard in deep and rugged train. It's very windy out there, it's very dry, and they are doing everything that they can to reduce the size of this fire as soon as possible," Mike Theune, the Park Service's information officer for the Santa Rosa Island Fire, told SFGATE.
After days of high winds and dry weather, winds are expected to weaken on Tuesday, and humidity is expected to increase.
The island is the second-largest of the Channel Islands and home to rare plant species, including six found nowhere else in the world. Located about 26 miles off the California mainland, it's largely uninhabited except for Park Service staff who have housing on the island.
While the fire is the largest to ignite in the state this year, multiple blazes have popped up in recent days, forcing firefighting personnel and resources to be dispersed across the state.
"Today new wildfires ignited on the mainland which immediately became the priority," the Park Service's incident overview stated Monday. "Per policy, firefighting resources are always assigned based on the greatest threats to life, safety, and property. This prioritization helps ensure that the most urgent needs are addressed first during rapidly evolving fire activity."
Theune said there has not been any delay in getting resources after the other wildfires started throughout the state.
"We're going to keep requesting as many wildland firefighters as we need," he said.
Former Channel Islands National Park Superintendent Russell Galipeau told SFGATE via phone that he's been following news of the fire closely and is concerned that specialized fire trucks haven't yet arrived on the island, saying: "Why is it taking this long?"
National Parks Bureau Chief Ashley Harrell contributed to this report.
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