MARTINEZ, Calif. — A twisted rapist telephoned the victim’s dad and sadistically boasted about the sexual assault happening on his end of the line, according to shocking testimony heard in California.

Two men are on trial in Contra Costa County, accused in a horrific gang rape of a 16-year-old girl who was brutalized outside her high school homecoming dance.

The victim’s dad – identified only as John Doe to protect his daughter’s identity – told jurors yesterday that he was on his way to Richmond HS, about 18 miles northeast of San Francisco, to pick up his daughter when he received a call from her cell phone.

A male voice described, in vulgar terms, what was happening to his daughter. The dad said he wanted to believe the call was a sick prank.

“I’m envisioning it and it was a horror,” the dad told jurors.

Jose Montano, 22, of Richmond and Marcelles Peter, 20, of Pinole are both charged with forcible rape, rape by foreign object and forced oral copulation. If convicted, they face life sentences.

The shocking gang rape could have involved up to 20 men who also punched, dragged, and urinated on the victim, Deputy DA John Cope said.

Montano and Peter are the first of six men initially charged to face trial. Two others are awaiting trial while two more took plea bargains.

When the victim’s dad rolled up to the school, he saw police cars screaming past him before he spotted his badly injured daughter. The dad told jurors he could barely recognize his daughter on the paramedic’s gurney.

“Her face was distorted, no longer round,” he said. “Ashen, gray, pale, clammy. She seemed to me on Death Row.”

Under cross examination, the emotional dad recounted how he told his little girl, “that we loved her and for her to hold on.”

Prosecutor Cope has told jurors the cops were called to the school when they found the drunk, incoherent girl with her body scratched, bruised and almost completely nude.

The defense claims authorities don’t have enough evidence to tie their clients to the disgusting assault.

The men are being tried together, but in front of two separate juries. They’ll hear the same evidence but deliberate in two different rooms, each weighing the fate of one defendant.

Montano’s DNA was found on a nearby condom wrapper and can of alcohol – but not on the victim, cops said.

The victim is expected to testify in this trial, but Cope said she doesn’t remember the attack.