Investigators are searching for multiple suspects in the fatal shooting of seven people at a large, illegal marijuana cultivation and processing site in Southern California's rural foothills
The crime scene in the community of Aguanga, about 160km southeast of Los Angeles, was discovered by sheriff's deputies responding early on Monday to reported assault with a deadly weapon, Riverside County Sheriff Chad Bianco said.
Six victims were found dead in and around a single dwelling on the sprawling property. A seventh victim, a woman still alive when deputies arrived, died later at a local hospital, Bianco told a news conference.
Sheriff's detectives assisted by federal agents were still combing the site for evidence and interviewing witnesses.
"We believe at this time that there were multiple suspects," he said.
More than 20 people lived at property, a "major organised crime-type operation" consisting of multiple homes and other buildings, including a cannabis nursery and facilities for drying and processing marijuana plants, the sheriff said.
"All of the people that were on the site, that were potential witnesses or the victims, were Laotian," he added, without elaborating on their ethnicity or immigration status.
Investigators seized more than 450kg of processed marijuana with a street value of $US1 million to $US5 million ($A1.4 million to $A6.9 million), along with a couple of hundred live cannabis plants and a lab for extracting cannabis oil from them.
While marijuana remains classified as an illegal narcotic under US federal law, California in 2018 legalised possession and use of marijuana by adults for recreational purposes, as well as commercial cultivation and distribution by businesses specially licensed and regulated by the state.
But a marijuana black market still thrives, posing what law enforcement considers an ongoing public safety threat.