CHEYENNE, Wyo. (AP) - A Wyoming landmark will grace one of the stamps in the U.S. Postal Service's new "Wonders of America" series.

Yellowstone National Park's Steamboat Geyser - the world's tallest active geyser - is one of 40 stamps in the collection. Another stamp will feature the Rocky Mountains as the world's longest mountain chain.

Other area stamps in the collection include two from Colorado: Cliff's Palace, the largest cliff dwelling in Mesa Verde National Park, and Great Sand Dunes National Park, which is recognized as having the tallest sand dunes.

The stamps were unveiled Saturday in Washington at the opening of the World Philatelic Exhibition, the world's largest stamp show.