Designating the country's newest national monuments, President Barack Obama said Thursday that protecting places of natural beauty and historic significance is a truly American ideal.

Obama used the powers of the presidency to designate the Pullman National Monument in his hometown. The historic South Side neighborhood is where African-American railroad workers won a significant labor agreement in the 1930s that Obama said led to such protections as the 40-hour work week.

"So this site is at the heart of what would become America's labor movement," he said.

Pullman workers also played a role in the rise of the black middle class.

Obama began his career as a community organizer nearby and said returning to designate the monument "brings back a lot of good memories."

Before leaving Washington, Obama signed a proclamation in the Oval Office designating the Browns Canyon National Monument in Colorado, a 21,000-acre site along the Arkansas River popular for whitewater rafting. In Chicago, he also announced designation of the Honouliuli National Monument in Hawaii, the site of an internment camp where Japanese-American citizens and prisoners of war were held during World War II.

"Conservation is a truly American ideal," Obama said. "The naturalists and industrialists and politicians who dreamt up our system of public lands and waters did so in the hope that by keeping these places, these special places in trust, places of incomparable beauty, places where our history was written, then future generations would value those places the same way as we do."

Obama also announced a new program to provide fourth-graders and their families with free admission to national parks for a year.

The Pullman designation honors the neighborhood built by industrialist George Pullman in the 19th century for workers to manufacture luxurious railroad sleeping cars. The 203-acre Pullman site includes factories and buildings associated with the Pullman Palace Car Company, which was founded in 1867 and employed thousands of workers to construct and provide service on railroad cars. While the company employed a mostly white workforce to manufacture railroad passenger cars, it also hired former slaves to serve as porters, waiters and maids on its iconic sleeping cars.

The railroad industry -- Pullman in particular -- was one of the largest employers of African-Americans in the United States by the early 1900s. Pullman workers played a major role in the rise of the black middle class and, through a labor agreement won by the Brotherhood of Sleeping Car Porters, they helped launch the civil rights movement of the 20th century, the White House said.

The new monuments bring to 16 the number of national monuments Obama has created under the 1906 Antiquities Act, which grants presidents broad authority to protect historic or ecologically significant sites without congressional approval.

Some Republicans have complained that Obama has abused his authority. They renewed their complaints over the newest designations, especially the Colorado site, the largest in size by far among the three new monuments.

Obama should "cut it out," said Rep. Ken Buck, R-Colo. "He is not king. No more acting like King Barack."

Rep. Doug Lamborn, R-Colo., called the move a "top-down, big-government land grab by the president that disenfranchises the concerned citizens in the Browns Canyon region" in central Colorado, about 140 miles southwest of Denver.

Outdoors and wildlife groups applauded the Browns Canyon designation, saying it would allow future generations to enjoy its spectacular landscapes, world-class whitewater rafting, hunting and fishing.

Illinois' senators, Democrat Richard Durbin and Republican Mark Kirk, hailed the Pullman designation.

"As Chicago's first national park, Pullman's 135 years of civil rights and industrial history will be protected and enjoyed for generations to come," Kirk said. He said the new park would bring up to 30,000 visitors and more than $40 million annually.