Washington ? Congress’ efforts to convert the tallest sand dunes in North America into a Colorado national park and wildlife refuge took a big step Wednesday with a private conservation group buying a huge ranch next to it.

The Nature Conservancy said it is spending $31.28 million to purchase the 97,000-acre Baca Ranch and two 14,000-foot peaks in southern Colorado, next to Great Sand Dunes National Monument and Preserve. The ranch’s plentiful aquifer keeps the 750-foot-high dunes intact and nourishes the San Luis Valley’s farmers and ranchers.

The conservation group’s purchase prevents the land from being sold to someone else. Once the deed is turned over to the federal government, the 38,700-acre monument and preserve will be combined with most of the ranch, including Kit Carson Peak and Challenger Point, to become Great Sand Dunes National Park and Preserve.

Part of the ranch will become Baca National Wildlife Refuge, where hunting will be allowed.

“This project represents conservation and partnership at a truly heroic scale,” said Steve McCormick, the group’s president.

The last time Congress created a national park was in 1999 with the conversion of another Colorado national monument into Black Canyon of the Gunnison National Park. Great Sand Dunes would be the nation’s 56th national park.

Interior Secretary Gale Norton said Wednesday she strongly supports its creation in her home state, where she was Colorado’s attorney general before joining the Bush administration.

Colorado Gov. Bill Owens said the ranch purchase is the largest land preservation effort in the state’s history and would protect “the history, culture and way of life of the entire San Luis Valley.”

Once the park is created, Colorado’s Taylor Peak would be the only remaining 14,000-footer left in private hands in North America.