The Sunday night blaze was reported by neighbors of the vacant vacation home, according to the Santa Cruz Sentinel.
Neighbors reported seeing flames as well as a partially nude young woman staring at the blaze from the back deck.
"It is going to be hard to determine a cause because there is so much damage," Fire Inspect Mike DeMars said.
The woman, 20, at the scene was topless and was unable to tell firefighters and other authorities why she was there and has been hospitalized.
Firefighters were able to contain the blaze and stop it from spreading to other homes.
No injuries have been reported.
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