An enormous sea of shifting sand, an American Sahara deposited at the base of the Rocky Mountains by 12,000 years of southwesterly winds, became the nation's newest national park Monday as Interior Secretary Gail A. Norton guaranteed permanent protection for a unique geological phenomenon that had been threatened by commercial speculators.

Great Sand Dunes National Park, an improbable swath of swirling khaki desert amid white-capped mountains and dark green forests just north of the Colorado-New Mexico border, becomes the 58th national park. It is a rare park because the Great Sand Dunes have no hiking trails; any designated trail would blow away with the next wind. Rather, rangers point visitors toward the tallest of the dunes -- it is half again as high as the Washington Monument -- and say, "Start climbing."

The new park is the first one created under the Bush administration. The enabling legislation was passed under President Bill Clinton, but it took four years to resolve land-control issues in a park and adjacent wildlife refuge that cover nearly three times the land area of the District of Columbia.

As with most land-use disputes in the arid southwest, the effort to protect this windswept desert revolved around water. The Great Sand Dunes are kept in place by a series of rivers that provide the sand and form the borders of the sandy field.

For a quarter-century, private companies have bought subsurface water rights here in the San Luis Valley, with plans to sell the water to thirsty western cities. Geologists and conservationists warned that draining the water table would endanger the highest formation of sand dune in North America. The national park designation, and accompanying federal land acquisition, means the water -- and the dunes -- will stay in place.

Geologists say the Great Sand Dunes began forming at the end of the last ice age, 12 millennia ago. The headwaters of the Rio Grande carried sand down the San Juan Mountains to the open bowl of the San Luis Valley. The prevailing southwesterly winds, blowing at an average of 35 mph, carried the sand about 60 miles -- until it ran into a natural trap, the imposing wall of the Sangre de Cristo Mountains.

Although the crests and troughs are reshaped by each shift of the wind, the overall pattern of tawny dunes across the sky looks much the same today as it does in photos from a century ago.

As early as the 1920s, the women's organization PEO began pushing for permanent protection for the dunes. In 1932, President Herbert Hoover made part of the area a "national monument," a designation that bars development to some degree.

But that legal status was not enough to keep out the water companies that developed expansive plans to pump water from beneath the San Luis and pipe it to Los Angeles, Phoenix or Denver. These projects prompted major political and legal battles.

"When you say 'water speculator' in this valley, people start fighting," Sen. Ben Nighthorse Campbell (R-Colo.) observed at today's ceremony.

The key impetus for tighter protection, park officials say, came when a Park Service geologist, Andrew Valdez, cornered then-Interior Secretary Bruce Babbitt in the late 1990s. "I told him we have to acquire and protect this entire geological system, about 300 square miles of it, or we'll eventually lose the dunes," Valdez recalled.

Babbitt pushed the national park legislation through Congress in 2000, but tight federal budgets since then meant the National Park Service could not fund the $32 million needed to buy surrounding land and water rights. A private group, the Nature Conservancy, came up with the money and sold the lands over time to the government.

"Today, we own the land, we own the water, and this sandy gem is safe," Norton declared here today.

Visitors to the sand dunes -- about 300,000 per year, the Park Service says -- tend to hike high up the dunes, jump off the steep cliffs and "act out their favorite scenes from desert movies," said the park superintendent, Steve Chaney. Many come with sleds, skis or snowboards to slalom down the sand.

But the chief attraction seems to be sheer wonder of a Lawrence-of-Arabia environment in the midst of the mountains. Although much of the nation's southwest is designated as "desert," American deserts are generally covered with scrub brush, grasses and wildflowers.

The dunes have been startling passersby at least since 1807, when Army Col. Zebulon Pike sent word back to Washington that he had discovered a world of "sandy hills . . . exactly like that of a sea in a storm except as to its color, and not a sign of vegetation."

National Park Service Director Fran Mainella, who came to inspect her newest park, expressed a standard sentiment for first-time visitors: "I had seen pictures, and I thought it would be nice," she said. "But this place isn't nice. It's awesome."

Great Sand Dunes National Park, a desert at the base of the Rocky Mountains, will be protected from commercial interests that sought the rights to water near the dunes.