An autopsy was being conducted Monday on a 13-year-old Sonoma Valley girl who died unexpectedly late Saturday night.

Her death is under investigation by the Sonoma County Coroner's Office because of the mystery involving what could have killed the Agua Caliente girl.

Sheriff's Lt. Dennis O'Leary Monday said the girl was found in her bedroom by family members.

She was unresponsive and they called for help at 10:08 p.m. Within 20 minutes sheriff's deputies were called to the hospital to look into her death, according to sheriff's reports.

The girl, whose name was being withheld by sheriff's officials, had been fine all day.

Minutes before she was found she'd taken some food into her bedroom, O'Leary said.

There was no sign of trauma or foul play or obvious signs of what could have happened, he said.

Sheriff's officials were hoping Monday's autopsy would show what had occurred.