As you enter Wyoming from the east, the plains begin to roll like ocean swells, rising and falling until they break against the Rockies. As the elevation rises, the grass grows shorter. Rains taper from dependable downpours to sporadic cloudbursts. The wind races across the surface, combing down the grass and sculpting the snow.

Bison once roamed these prairies in enormous herds, and people were few. But the modern era brought rapid change. In the 18th century, Indian bands mounted horses that had escaped from Spanish conquistadors and enjoyed a brief era of prosperity on the plains, hunting buffalo with great skill. Then the white people arrived: trappers searching for beaver pelts, and pioneers who wanted to either settle here or just pass through on their way to Utah, California, or Oregon. But it was the Texas trail drives, moving north, not west, that most shaped the history and culture of eastern Wyoming.

The landscape hasn't changed much since then. There are still widely scattered settlements; a few small, irrigated fields; and lots of grass and cattle. The billboards announce WELCOME TO THE COWBOY STATE, but these days it's more often the coal and oil and gas beneath the prairies that subsidize the human population in these wide-open spaces. But the cowboy life is still vibrant and friendly to visitors: You can see rodeos or join a cattle drive, or just buy a hat and pair of boots and pretend. You can explore the mostly unchanged landscapes where cattle barons and their hired guns battled homesteaders in the Johnson County War, where outlaw Butch Cassidy and the Hole-in-the-Wall gang did their "work," and Indian chiefs Crazy Horse and Red Cloud clashed with the cavalry.

Adventurers come to climb Devils Tower, a natural skyscraper of volcanic rock that suddenly rises more than 1,000 feet from the flatlands of eastern Wyoming. Visitors also come to hike and fish in the Bighorn Mountains, a handsome range somewhat overshadowed by the peaks of the Continental Divide farther west.

You can explore this region by interstate -- I-25 runs north-south, while I-90 dips down from Montana and then east to Gillette and Devils Tower -- or take small highways like U.S. 18 and Wyo. 59 to reach smaller towns and more remote country.