GREAT SAND DUNES NATIONAL MONUMENT'S vast dunes in southern Colorado -- the highest in North America -- can tower as high as 700 feet, a natural wonder owned (and paid for) by all Americans since 1932, when President Hoover proclaimed them a National Monument.

In the summer, sand temperatures can reach 140 degrees Farenheit -- almost twice as high as the average temperature of the air. At night, the air temperature may drop into the 40s.

The Park has 18 miles of established trails away from the dunes, and 39 square miles of unlimited hiking on the dunes themselves. In spring and early summer, the Medano Creek flows along the dunes' edge.

Photo: Chris J. Calwell