Colorado lawmakers who helped double the number of national parks in the state during the past two decades agree the state’s national parks are treasures in economic and symbolic ways.

But the conversation on public lands becomes more complex when talking about the future. The days of designating large, new national parks may be gone for an agency that struggles under budget constraints, and granting special protections for public lands is getting more contentious.

As the National Park Service celebrated its centennial this week, The Denver Post interviewed four former senators from Colorado to discuss their involvement in creating national parks and their perspectives on protecting public lands. These leaders fought together for new national parks, but their views on protecting other federal lands are less uniform.

“As the nation grows, those areas that have been set aside for everyone’s use are becoming more and more valuable, not only from an economic standpoint, but also from a heritage standpoint,” said Ben Nighthorse Campbell, a Republican for most of his 12 years in the U.S. Senate.

Campbell led the effort to designate the Black Canyon of the Gunnison as a national park in 1999, a push motivated by a developer’s threat to build homes at the edge of what was then a national monument.

Ken Salazar, a Democratic U.S. senator from 2005 to 2009 who later served as secretary of the interior, said national parks serve a vital role in supporting local communities. He also defended the Obama administration’s push to establish national monuments without congressional approval.

“Here in Colorado, one could think about Rocky Mountain National Park or the Great Sand Dunes down in the San Luis Valley, and they’re huge economic drivers for our state,” he said. “Thousands and thousands of jobs are created from the fact that we have those crown jewels in our state.”

But Wayne Allard, a Republican who served in the Senate from 1997 to 2009 and worked with Campbell and other Colorado lawmakers on the Great Sand Dunes designation, drew a distinction between national parks and other types of public lands.

Allard said many small communities — including those in the San Luis Valley that pushed for national park status — rely on national parks “because so much of their economic growth depends on how those lands are managed.” For other types of public lands, however, “far reaching” proclamations to establish national monuments need to be handled through legislation instead, he said.

“I think it needs to go through the Congress, and there needs to be local input on whether that’s desirable or not for that area,” Allard said. “If you tie something up, where there’s no access to the area, then you begin to hurt the economy of the small towns in those areas.”

Many Republicans opposed the designation last year of Browns Canyon as a national monument. President Barack Obama created the monument through a proclamation under the Antiquities Act, fulfilling a long-standing effort by some of Colorado’s congressional delegation.

The monument is not managed by the park service, as some monuments are — and unlike national parks, monuments can be designated by a presidential order. But the battle to protect the area along the Arkansas River between Buena Vista and Salida was indicative of a pushback among some lawmakers to the creation of any new public lands.

Mark Udall, who served in the Senate from 2009 to 2015, introduced legislation to designate Browns Canyon as a national monument at the end of 2013. His bill met opposition by what he deemed to be a determined “small minority” of members in Congress.

“We could have passed that bill out of the Senate, I have no doubt,” Udall said. “But it was going to be dead on arrival in the House of Representatives, in part because of the chairman of the House Natural Resources Committee and just the mindset over there that ‘we’re not going to protect any more lands as wilderness and we’re not going to create any more national monuments.’ And it’s based, from my point of view, on an ideological rigidity which doesn’t reflect the broad public support for greater protection of our public lands when it’s appropriate.

“So after building all of that support and making the case through the legislation, it gave the president the confidence that this (national monument designation) was the right thing to do.”

Obama often has used the Antiquities Act — a 1906 law allowing presidents to preserve lands with natural or cultural value — as he established 24 national monuments during his presidency, including Browns Canyon and Chimney Rock in Colorado in 2012.

Some Republicans have criticized Obama’s use of the act, pointing to the fact that he has created more national monuments than any previous president and saying he is exceeding its original intent.

But Salazar said the act is a nonpartisan approach used by almost every president since Teddy Roosevelt to set aside public lands. “I think it’s especially a very useful tool when you have a Congress that’s essentially in gridlock on the passage of legislation,” Salazar said.

As interior secretary from 2009 to 2013, Salazar worked with Obama to create 10 national parks and 10 national wildlife and conservation areas, along with other public lands across the nation.

This pushback against public lands has garnered increased attention, following the occupation of the Malheur Wildlife Refuge in Oregon this year by a group protesting the government’s management of these areas.

As the Republican Party worked on drafting its 2016 platform before its convention, it also included a passage calling for federal land transfers that would give certain public lands to states.

Salazar called the GOP’s proposal “wrongheaded,” saying “our public lands should be supported and not given away or ceded.”

Colorado U.S. Sens. Michael Bennet, a Democrat, and Cory Gardner, a Republican, are moving forward with legislation to strengthen the state’s federal public lands.

According to Bennet’s office, the senator has been working in part on legislation that would designate Curecanti National Recreation Area as a unit of the park service, a move that has not yet been formally done. And he’s also working on legislation to make Camp Hale outside of Vail the first National Historic Landscape, as well as legislation to establish several new wilderness and special management areas across the state.

Gardner introduced legislation in June that would allow a private landowner to donate land to the Florissant Fossil Beds National Monument.