U.S. Senate Democrats rolled up their sleeves on Sunday, overcame stalling tactics” by some Republicans, and advanced legislation to protect more than two million acres of wilderness in nine states, including some in Colorado.

The massive bill was the largest expansion of protections for lands across the nation in 25 years, writes The Washington Post, including Rocky Mountain National Park, which will be protected forever if the legislation passes.

The bill’s sponsor, Senator Jeff Bingaman, a Democrat from New Mexico, says the bipartisan bill is years in the making, although some members of the GOP are upset that it cannot be amended.

Meanwhile, the Rockies’ regional director of The Wilderness Society is happy, calling the bill a “major step in protecting some of Colorado’s priceless landscapes,” according to the Rocky Mountain News.

Senator Ken Salazar, who has been tapped as the nation’s next interior secretary, supported the bill. Formal Senate approval is expected later this week before the legislation moves to the House.