PALMDALE, Calif. -- An investigation was under way Friday into the slaying of a popular middle school girl whose body was wrapped in a rug and dumped into a ditch beside an onion field in a remote area east of Palmdale.

The body of 13-year-old Stevona Campbell of Palmdale was discovered at about 6:45 a.m. Monday on Avenue P, between 40th Street East and 50th Street East, said Ed Hernandez of the Sheriff's Headquarters Bureau.

Her death has been ruled a homicide, but the cause of death has yet to be determined, said Lt. John Kadas of the coroner's office.

"An autopsy has been performed, but the results aren't back yet," Kadas said early today, adding he did not know when they would be available.

Stevona was last seen Sunday night when she attended a large Mother's Day party at her family's apartment in east Palmdale, the Los Angeles Times reported.

She left the party around 7 p.m. -- disobeying her mother's orders to stay home -- and never returned, family members told the newspaper.

On Monday morning a farm worker discovered Stevona's body wrapped in a rug in a ditch beside an onion field east of Palmdale, about a mile away from a shopping center under construction, the Times reported.

Family members described the victim as a popular student at Cactus Middle School in east Palmdale.

"She was full of energy, a regular 13-year-old ... the center of attention," Stevona's cousin, Lacreasia Chambers, told the Times. "She didn't deserve this."

Anyone with information about the case was urged to call the sheriff's department at 323-890-5500.