ALAMOSA, COLO. — Sand hiking isn't easy.

For every step upward, you slide half a step downward in the giant sandbox.

It's tough, gritty hiking but it's the best way to really get a glimpse of the 750-foot-high dunes that are the big attraction in America's newest national park in southern Colorado.

And that's lots of sand, nearly 40 square miles of massive dunes.

Great Sand Dunes National Park and Preserve — the country's 58th national park — was officially created in late 2004, although President Bill Clinton signed the legislation setting the process in motion in late 2000.

The new national park had been a national monument. It was just under 43,000 acres when it was created in 1932. It was enlarged to 107,451 acres.

An adjoining preserve of 41,686 acres was created.

The new federal designation was granted after the federal government gained control of the 97,000-acre Baca Ranch that lies to the west of the dunes. The Nature Conservancy helped with that purchase.

One-third of the ranch was added to Great Sand Dunes, but most of it became a new federal wildlife refuge. The park also grew with the addition of two ranches to the south and portions of the Rio Grande National Forest to the east. Some U.S. Forest Service land was also added to Great Sand Dunes. The acquisition of 151 square miles of land helped preserve the ecosystem that surrounds the dunes.

The dunes, the tallest in North America, extend more than six miles to the north and west from the park's visitor center and campground.

The dunes spread across the eastern side of the San Luis Valley. It is a 50-mile-wide swath of ranch land 8,200 feet in elevation.

The dunes — clearly visible as brown waves 20 miles away — are tucked next to the 13,000-foot-high peaks of the pine-covered Sangre de Christo (Blood of Christ) Mountains.

The dunes were created when winds carried sandy particles from the San Juan Mountains that were deposited by the Rio Grande River.

The sand particles are trapped at the foot of the Sangre de Christo Mountains by countering winds that blow down the mountain valleys. Two creeks flowing out of the mountains provide an added barrier.

One of the best ways to see the park is to get out into the dunes. There are no trails. You can hike anywhere you want.

Not far from the park's visitor center is the High Dune. It's not the tallest in the dune field, but is among those that have the highest elevation above sea level.

High Dune — about 650 feet from base to top — is one of the most accessible of the park's big dunes.

The sand is soft and the slopes are steep — as much as 32 degrees. To get to the top is a moderately strenuous hike as you zigzag up the dune's ridge lines. There is a great view from the top. That's your reward.

Getting down is much easier. Some folks ski down or ride sand boards. The best conditions for that are when the sand is cold, from October through April.

The wind-shaped dunes and sand patterns are strikingly colorful and pretty, especially in the soft light of early morning and twilight. The dunes also are popular for nighttime walks when the moon is full.

Dune walking is fairly simple. Leave your shoes on. Sand temperatures in the summer can hit 140 degrees. Hot and rough sand can blister feet.

Distances in the dunes are deceiving. Things are often farther away than they appear.

Summer temperatures are in the 70s and 80s, dropping into the 40s at night.

Dunes have two slopes or faces. The shallow, gentle side is the windward face. Sand blown from the windward face is deposited on the steep leeward side. Sand avalanches result when the slopes get too steep.

The dunes remain largely in place due to reversing storms and the moisture in the sand.

The Colorado dunes attract about 280,000 visitors a year. But there's more to the park. Some trails lead up into the mountains, with their alpine meadows, rugged canyons, waterfalls and lakes.