David Allen Turpin, 57, and Louise Anna Turpin, 49, were held on charges of torture and child endangerment.
The 13 people – aged between two and 29 – were found in a house in Perris, 59 miles (95km) south-east of Los Angeles, police say.
They are all believed to be siblings.
Officers were alerted by one of the victims, who on Sunday managed to escape and call the emergency number “from a cellular device she found inside the house”, the Riverside Sheriff’s Department said in a statement.
The girl – who police said appeared to be “only 10 years old and slightly emaciated” – claimed that 12 of her siblings were being held captive by their parents.
Police officers later found “several children shackled to their beds with chains and padlocks in dark and foul-smelling surroundings”.
But the parents were unable to immediately provide a logical reason why their children were restrained in that manner, the police said.
The officers were “shocked” to discover that seven of those held in the house were actually adults aged between 18 and 29.
“The victims appeared to be malnourished and very dirty,” the police said.
All the victims are now being treated in local hospitals.
The head of one of the hospitals, Mark Uffer, told Reuters news agency: “It’s actually heartbreaking for the staff and it’s unbelievable what you see.”
One neighbour told Reuters that the Turpin family “were the type that you didn’t really get to know anything about them”.
“You would never see them on visit, you would never see anyone come outside. All you would really see is that they go out and maybe do a grocery round. And that was about it,” the neighbour added. (Courtesy BBC)