During a search on Thursday night, police found an underground shooting site at the Fontana home of a well-known gang member.
The anti-terrorist unit of the gangs has found a hole in the house, which can lead to the shooting.
The statement said the officers found "a lot" of weapons and thousands of shots, including a 100-hour drone for the AR-15.
An unspecified number of suspects were arrested without and detained. Their names are not disclosed.
"We will never give up on keeping our community safe and free from violence," said the police statement. "We are the hide-and-seek champions, and if you hide, we'll find you, and if you run, you'll go to jail tired."