BURNS, Ore. -- After the last four occupiers of a national nature preserve surrendered Thursday and a leader in their movement criminally charged in federal court, the FBI said the public land will remain closed for several weeks as authorities inspect the area and gather evidence.

At a news conference, Greg Bretzing, FBI special agent in charge in Oregon, said authorities would examine buildings at the refuge to ensure nobody else was hiding out. After that, he says specialized teams would look for "explosive-related hazards." He said that could take several days.

The last four occupiers at the Malheur National Wildlife Refuge surrendered Thursday, ending an occupation that began Jan. 2.

The holdouts were the last remnants of a larger group that seized the Malheur National Wildlife Refuge nearly six weeks ago, demanding that the government turn over the land to locals and release two ranchers imprisoned for setting fires. For the first time since Jan. 2, the federal land was fully under the control of the U.S. government.

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Meanwhile, Cliven Bundy, who was at the center of the 2014 standoff at his ranch in Nevada, was arrested late Wednesday in Portland after encouraging the Oregon occupiers not to give up. Bundy is the father of Ammon Bundy, the jailed leader of the Oregon occupation.

On Thursday, the elder Bundy was charged in the standoff from two years ago. Federal authorities may have feared Bundy's presence would draw sympathizers to defend the holdouts.

The 69-year-old Bundy was charged with conspiracy, assault on a federal officer, obstruction, weapons charges and other crimes. He's accused of leading supporters who pointed military-style weapons at federal agents trying to enforce a court order to round up Bundy cattle from federal rangeland.

It was not immediately clear if he had a lawyer ahead of a court appearance in Portland.

Federal authorities say the Bundy family has not made payments toward a $1.1 million grazing fee and penalty bill.

The FBI said the final four occupiers were arrested as they walked out of the refuge to the FBI checkpoint. No one was injured and no shots fired.

Federal authorities were criticized during the occupation for not ending it sooner. But some experts said the FBI's strategy of letting the tensions die down before moving in ensured there would be no bloodshed.

"This was beautifully executed," said Brian Levin, a criminal justice professor at California State University, San Bernardino. "This siege and the way it was handled will go down in law enforcement textbooks."

It was unclear what effect the occupiers' presence had on the refuge or any of its archaeological artifacts. Videos posted online showed members of the armed group exploring buildings at the site and criticizing the way tribal artifacts were stored there.

Outside, the videos sometimes showed group members in tents or gathered around a campfire, driving vehicles and setting up barricades. They erected a canopy next to a pickup truck and an old car and put camping chairs and coolers around it. The area appeared strewn with plastic water bottles, cardboard boxes, clothes, packages of bullets and beer cans.

The last four occupiers were scheduled to be arraigned Friday in Portland. The holdouts and 12 others connected with the Oregon occupation have been charged with conspiracy to interfere with federal workers.

The occupiers were 27-year-old David Fry of Blanchester, Ohio; Jeff Banta, 46, of Elko, Nevada; and married couple Sean Anderson, 48, and Sandy Anderson, 47, of Riggins, Idaho.

The FBI began moving in Wednesday evening, surrounding their encampment with armored vehicles. Over the next several hours, the occupiers' panic and their negotiation with FBI agents could be heard live on the Internet, broadcast by a sympathizer of the occupiers who established phone contact with them.

Fry, an Ohio resident, said he was declaring war against the federal government.

The Andersons and Banta surrendered first on Thursday. Fry initially refused to join them.

"I'm actually feeling suicidal right now," Fry told the sympathizer, identified on his YouTube channel as Gavin Seim, and KrisAnne Hall, an activist who was also on the call.

"I'm making sure I'm not coming out of here alive," Fry said at one point in the Thursday livestream. "Liberty or death, I take that stance."

After ranting for a while, he too surrendered.

After the arrests, Gov. Kate Brown thanked authorities on Twitter.

So relieved this ordeal is over. Many thanks to law enforcement who brought the Harney County occupation to a close. 1/2 — Kate Brown (@OregonGovBrown) February 11, 2016

Now, let's focus efforts on helping this community recover, including the Burns Paiute Tribe. 2/2 — Kate Brown (@OregonGovBrown) February 11, 2016

A Nevada lawmaker was key in getting them to give up. Michele Fiore is also a friend of the Bundy family. She came to Portland on Wednesday to show support for Ammon Bundy. When she heard the FBI had surrounded the refuge, she called into the online talk show to try to calm down the occupiers.

Fiore rushed to Burns to help negotiate a peaceful surrender of the occupiers.

The Oregon standoff began when Ammon Bundy and his followers took over the refuge south of Burns. Federal agents, Oregon state troopers and sheriff's deputies monitored the occupation to avoid a confrontation. As the weeks passed, there were growing calls for the FBI to act, including from Brown.

They did, on Jan. 26. On that day, Ammon Bundy and other occupation leaders were heading for the town of John Day to give a talk on federal overreach. FBI agents and Oregon state troopers stopped the group's two-vehicle convoy. Robert "LaVoy" Finicum was shot dead in that confrontation. The FBI says he was going for a pistol inside his jacket pocket. Ammon Bundy and four others were arrested.

A total of 12 people were arrested that week. Most of the occupiers fled the refuge after hearing they would not be arrested if they left quickly. Four stayed behind, saying they feared they would be arrested if they left.

Oregon elected officials rejoiced at the end of the long occupation but said it will take a while for the rural area to recover. Brown called the episode "very traumatic."

"The level of harassment and intimidation by folks who were staying in the Burns community was horrific," she said. "And the healing will take a long time."