Officers seized over 5 pounds of heroin, worth nearly $300,000, along with $120,000 in cash and five cars.
Local, state and federal agencies were involved in the six-month probe of a heroin-trafficking operation.
On Wednesday, after executing search warrants in Sylmar and Arleta authorities arrested three suspects.
"The rate they were doing business over a one-year period, that would equate to a $6-million-a-year business," said Simi Valley Police Lt. Dave Livingstone. "So it was a very significant cell that was shut down with our investigation."
Jose Carillo-Flores, 23; Joseph Ortiz, 20; and 39-year-old Jose Medina Zepeda have all been booked on charges including possession of illegal narcotics for sale.
"It's my understanding that these three individuals are from out of our town," said Simi Valley Mayor Bob Huber. "We want the word to go out loud and clear: You come across our borders to hurt our children, we're going to catch you and you're going to prison."
Investigators also seized more than $120,000 in cash and five vehicles.
In the last six months, several young people have died from heroin abuse in Simi Valley.