An Oregon rancher and his son who helped inspire an armed anti-government protest at a remote national wildlife outpost surrendered Monday to federal prison authorities in Terminal Island.

Dwight Hammond, 73, and his 46-year-old son Steven turned themselves in at the Federal Correctional Institution after spending time with relatives in Southern California, authorities said.

The ranchers were convicted three years ago of starting brush fires on federal property that they said were designed to prevent larger wildfires and to halt invasive plant species.

They served short federal prison sentences, but a judge ordered them back to prison for four years after finding that the time they served did not meet minimum-sentencing laws.

The occupation at the Malheur National Wildlife Refuge began Saturday after an estimated 300 protesters marched through the nearby town of Burns, Oregon.

Ammon Bundy, a rancher who is leading the occupation, said the Hammonds — whose attorney said “respect the rule of law” and have not endorsed the occupation — were persecuted because the federal government wants their land.

Bundy and his son have called on militia members from across the nation to join their occupation.

Their father, Nevada rancher Cliven Bundy, spearheaded a standoff with the government over grazing rights on federal lands in 2014.