Two Oregon ranchers whose plight inspired militia groups to occupy a federal wildlife refuge turned themselves in to a federal correctional institution in California on Monday to begin serving their sentences.

Dwight Hammond and his son, Steven, arrived at the federal prison in San Pedro, California on Monday afternoon, accompanied by several relatives. After hugging them goodbye, the two men walked into the prison to begin serving additional time, after a judge ruled that their original sentences for setting fires on land near Burns, Ore., leased to them by the Bureau of Land Management were insufficient.

OREGON-MILITIA/STANDOFF

A U.S. flag covers a sign at the entrance of the Malheur National Wildlife Refuge near Burns, Ore., on Sunday. (Jim Urquhart/Reuters)

​Dwight Hammond's niece, Karyn Gallen, said the family found the order to return to prison "unfathomable."

"There was a trial in 2012 and ... that was a very long and trying trial at the time and they were sentenced then and they served their time in 2013, so the circumstances that we're in now are just unfathomable and it's certainly an American tragedy," she told reporters gathered outside the prison gate.

"My uncle is 74 years old. He has been married for over 50 years, and there's a lot of people who do what we can on a daily basis to stay engaged with our family and have a livelihood, and that's everything that they've always been about from the beginning."

The Hammonds' case attracted a crowd of protesters who marched through the streets of Burns on Saturday to protest the prosecution. Following the march, some of the demonstrators drove to the nearby Malheur Federal Wildlife Refuge and set up camp around the headquarters building.

Ranching Standoff Protest

Protesters march in support of Oregon ranchers facing prison time for arson in Burns, Ore., on Jan. 2. (Les Zaitz/The Oregonian/Associated Press)

The armed militia group was led by Ammon and Ryan Bundy, sons of Nevada rancher Cliven Bundy. Their family ranch in Bunkerville, Nevada, some 130 kilometres northeast of Las Vegas, was the site of an armed protest against the U.S. Bureau of Land Management in April 2014.

Gallen said her family had no connection to the demonstrators and did not support their actions.

"The last 48 hours is in no way connected to the Hammond family," said Gallen. "The Hammonds have always been about family first and understanding their circumstances. I think it's important for Harney County and Burns, Oregon to show support, but it has always been the request of the family to keep that peaceful, keep the conversation going, keep the right people talking, people who can actually make a difference."

'Go home to your families'

Harney County Sheriff David Ward on Monday called on the demonstrators to end their occupation.

"You said you were here to help the citizens of Harney County. That help ended when a peaceful protest became an armed occupation," he told a news briefing in Burns. "The Hammonds have turned themselves in. It's time for you to leave our community, go home to your families and end this peacefully."

But Ammon Bundy told reporters that the group believes the acquisition of the wildlife refuge by the federal government is unconstitutional and said the group plans to stay until the government gives up its claim to the land.

Schools in the small town of Burns, about 50 kilometres from the refuge, were closed for the week out of concern for student safety.

On Monday, the federal government was doing nothing to remove the group but the FBI said it was monitoring the situation. The White House said President Barack Obama was aware of the situation and hopes it can be resolved peacefully.

The refuge was established in 1908 by President Theodore Roosevelt to protect bird populations that had been decimated by plume hunters selling feathers for the hat industry.

It sits in a wide snow-covered valley rimmed by distant mountains and contains lakes and marshland. The preserve has grown over the years to about 480 square kilometres and surrounds the ranch Dwight Hammond bought with his father in 1964. Dwight Hammond said his family has resisted pressure to sell the ranch as the federal government chipped away at his grazing allotments and increased fees on other lands.

Ammon Bundy

Ammon Bundy, the son of Nevada rancher Cliven Bundy, is one of a group of people occupying the headquarters of the Malheur National Wildlife Refuge. (Les Zaitz/The Oregonian/Associated Press)

The refuge contains about 10 small buildings, some of which had been entered by the occupying group. Other members of the group blocked the entrance to the headquarters.

The takeover prompted an outcry far beyond Oregon from both those who want to see federal lands opened to more ranching and logging and others who were astounded that private citizens with guns could seize government property without any intervention by law enforcement.

The tactics of the Bundys and the group were condemned by Democrats and Republicans alike.

Sen. Harry Reid, a Nevada Democrat who is familiar with the Bundys from their standoff in his state, said the group could not continue breaking the law, but that everyone should remain patient.

"These people say we want to return (the land) to the people," Reid said. "The people have it right now."

Republican presidential candidate Sen. Ted Cruz of Texas said he hoped the group would "stand down peaceably" with no violent confrontation "sooner rather than later."

Ammon Bundy said his group had sent a demand for "redress for grievances" to local, state and federal officials. The group, which included a couple of women and some boys and girls Monday, did not release a copy of its demands. Bundy would not say what the group would do if it got no response.

"We have exhausted all prudent measures and have been ignored," he said.

At the time of the Bundys' 2014 Nevada standoff, there were $1.1 million in outstanding grazing fees, and no payments have been made since then. The fees continue to accrue, although Bureau of Land Management spokeswoman Bev Winston couldn't give a specific updated figure on the debt.

The disputes harken back to a long-running struggle over public lands between some Westerners and the federal government, which owns nearly half the land in the West.

In the 1970s, during the "Sagebrush Rebellion," Nevada and other states pushed for local control over federal land. Supporters of that idea want to open more land available for cattle grazing, mining and timber harvesting.

Opponents say the federal government should administer lands for the widest possible uses, including environmental and recreational.

Bundy said the group plans to stay at the refuge as long as it takes.

Keith Landon, a longtime resident of Burns who works at the Reid Country Store, said he sympathizes with the Bundys' frustrations. Landon was a logger until the federal government declared the spotted owl a protected species in the 1980s — a decision that hurt the local logging industry.

"It's hard to discredit what they're trying to do out there," he said. "But I don't want anybody hurt."

With files from The Associated Press