Thick black smoke and flames were coming through the roof and windows of the single-wide mobile home at 475 El Capitan Way when firefighters arrived at about 3:40 p.m., fire officials said.
No one was home when the fire started, and it went undetected for a long time until neighbors and passersby noticed and called 911, officials said.
Because of the strong winds, the fire was also starting to burn the outside of another mobile home.
Firefighters prevented the flames from spreading to the second mobile home and controlled the fire by about 4 p.m. using three engines and one truck. There were no injuries, fire officials said.
The Rincon Valley Fire Protection District is investigating the cause of the fire.