Visitors to the Great Sand Dunes Park and Preserve climb up the edge of the 30-square-mile dune field on Saturday, June 25, 2016.

(Nathaniel Minor/CPR News)

The U.S. government on Tuesday delayed a decision on a contentious proposal to allow oil and gas drilling near Great Sand Dunes National Park in southern Colorado, saying it first wants to consult with the Navajo Nation, which owns land in the area.

The Bureau of Land Management had planned to sell drilling rights on 29 square miles of public land east of the park at a Sept. 6 auction, but Navajo officials requested a formal consultation, and the agency agreed.

The bureau said the land could still be offered at a future auction.

A spokesman for the Navajo Nation didn't immediately respond to emails seeking comment.

The Navajo reservation — in Arizona, New Mexico and Utah — doesn't include Colorado. But tribal President Russell Begaye told The Denver Post the Navajos consider the area near Great Sand Dunes park to be part of their ancestral lands and bought 26 square miles there last year.

"This land is sacred and the Navajo Nation will always protect the beauty and sacredness of the land," he told the newspaper in May.

Environmental groups opposed the sale of drilling leases, saying the land is too close to the park, a wilderness area and wildlife habitat. Some warned drilling waste or spills could threaten water quality.

"It doesn't make a lot of sense they would choose this location," said Kimberley Pope, an organizer for the Sierra Club in Colorado.

Some state and federal officials also raised questions.

Great Sand Dunes park officials were concerned about the effects drilling could have on air quality, noise and dark skies, according to Fred Bunch, the park's chief of resource management, who submitted written comments to the Bureau of Land Management about the potential sale.

The bureau oversees the sale of minerals under most federal land.

The Colorado land under consideration for drilling is about 200 miles south of Denver and reaches to within a mile of the park's eastern boundary. The sand dunes are about 4½ miles west, but mountains stand between the potential drilling sites and the dunes.

The park says its dunes are the tallest in North America, some more than 700 feet high. The dunes cover 30 square miles​.