Lyons told the Galveston County Daily News that the caretakers locked the place and would not let firefighters near the structure Saturday night.
Firefighters put a ladder to the second-story porch and went in anyway. Lyons says marijuana paraphernalia was everywhere. More than 100 plants were seized.
Deputies detained a suspect, who allegedly returned to try to destroy the drugs.
The cause of the electrical fire is sought.
San Leon is 30 miles southeast of Houston.
