Browns Canyon.

(Photo: CPR/Lesley McClurg)

Browns Canyon, a popular spot for rafting and other outdoors activities, will be declared a National Monument later this week.

Sen. Michael Bennet said President Barack Obama will make the declaration Thursday, using his authority under the Antiquities Act of 1906. In 2013, former Sen. Mark Udall had introduced a bill for canyon's designation that ultimately failed. Late last year, Bennet, Udall and Gov. John Hickenlooper appealed directly to the president to protect the canyon about 140 miles southwest of Denver.

“Browns Canyon contains a rugged and unique beauty that attracts outdoor enthusiasts from around the world to hike, camp, climb, and raft – all of which help generate millions of dollars for local economies," Bennet said in a statement. "Coloradans have been very clear they wanted this protection, along with assurances that existing uses will be protected. We’re glad the Administration heard those voices and provided those assurances.”

Rep. Doug Lamborn, who represents the area in the U.S. House, said he's "outraged" by the designation.

"This is a top-down, big government land grab by the President that disenfranchises the concerned citizens in the Browns Canyon region," Lamborn said in a statement. "I’ve heard from multitudes of local citizens whose concerns about grazing rights, water rights, outdoor recreation, and the inability of first responders to manage and fight wildfires in the area have never been addressed."

In 2013, Udall told CPR's Lesley McClurg that designating the canyon as a National Monument would be a "big deal" because it would protect the area from future development. Rafting, hiking and fishing on the Arkansas River are already a big draw -- 100,000 whitewater rafters alone visit the area annually. Rafting businesses in the area supported the designation because it would heighten the area's visibility to potential tourists, but off-road vehicle enthusiasts opposed the move.

Conservation groups lauded the move. Conservation Colorado said in a news release Wednesday that it has worked with other groups "for years to protect the stunning lands, wildlife, gold medal fishing and internationally-acclaimed whitewater rafting of Browns Canyon."