(Linda Davidson/THE WASHINGTON POST - The Harriet Tubman Historical Marker at Brodess Farm in Cambridge, Md. The farm, historically recognized as the abolitionist’s birthplace, is near the new national monument.) (Linda Davidson/THE WASHINGTON POST - The Harriet Tubman Historical Marker at Brodess Farm in Cambridge, Md.)

President Obama defied congressional opposition and designated five new national monuments Monday, using his executive authority to put historic sites and wild landscapes in a half-dozen states off limits to development..

The designations affect three areas managed by the National Park Service, including one honoring abolitionist Harriet Tubman and the Underground Railroad in Maryland and a collection of sites commemorating Delaware as the nation's first state. Obama also used his power under the 1906 Antiquities Act to protect two swaths of land under the Bureau of Land Management’s control: Washington’s San Juan Islands and New Mexico’s Rio Grande del Norte.

“These sites honor the pioneering heroes, spectacular landscapes and rich history that have shaped our extraordinary country,” the president said.  “By designating these national monuments today, we will ensure they will continue to inspire and be enjoyed by generations of Americans to come.”

House Natural Resources Committee Chairman Doc Hastings (R-Wash.), who has opposed the creation of new wilderness areas and national parks, questioned why the president would extend public lands protection at a time when the federal budget is under pressure.

“The Obama Administration not only sees the sequester as an opportunity to make automatic spending reductions as painful as possible on the American people," Hastings said in a statement, "it’s also a good time for the President to dictate under a century-old law that the government spend money it doesn’t have on property it doesn’t even own."

But Conservation Fund president Lawrence A. Selzer, whose group donated land to help create both the Harriet Tubman Underground Railroad National Monument and Delaware's First State National Monument, said nearly half of the nation's national parks started out as national monument designations. In the case of Delaware, the state's Mt. Cuba Center gave $20 million to the Fund so it could purchase the 1,100-acre property Woodlawn in Delaware and Pennsylvania and donate it to the National Park Service.

"This is by no means unusual," Selzer said. "The fact that the president is stepping forward and using his authority is a reflection of the support at the local level."

It remains unclear whether Obama will designate other national monuments in the future; last Congress marked the first one since 1966 which failed to designate a single new national park or wilderness areas. Even the three national moments Obama has designated on Park Service land will not become national parks without an act of Congress.

White House spokesman Josh Earnest told reporters Monday that "in terms of future decisions along these lines, I don't have anything to announce at this point."

He did challenge Hastings' suggestion that these new monuments would put a financial burden on taxpayers, noting that local communities often benefit from tourism once an areas has been designated. "And in terms of the immediate costs -- in terms of the management of the land, I think they're pretty minimal in the early stages," he said.

Mike Matz, who heads the Pew Charitable Trusts' Campaign for America's Wilderness, said there are several other large landscapes that enjoy significant local and bipartisan support. These include Idaho's Boulder-White Clouds proposed wilderness area and Cedar Mesa plateau in Utah.

Since the Rio Grande del Norte is the only large wild area Obama has declared a national monument so far, Matz said, "We would like to see him do more on that scale."

Republicans may try to repeal the Antiquities Act, though it is unclear whether they would succeed. Sen. David Vitter (R-La.) offered an amendment revoking the president's authority last week as part of the budget debate, but it didn't come up for a vote.