INDEPENDENCE ROCK, Wyo. – There is something strangely alluring about this place in the openness of Wyoming. Ranches go on for 20 miles, and motion comes primarily from the wind, oil derricks and 125-car coal trains.

But a giant rock that juts 120 feet out of the sagebrush has long provided a solid measuring point. Independence Rock stands a sentry over the history of the American movement west.

For a quarter-century before and after the Civil War, Independence Rock was the primary marker on the Oregon Trail. The rule was simple: If settlers coming out of St. Louis did not make this place by July 4, chances were they would not get through looming dangerous mountain passes before winter descended. Those who arrived thereafter often faced a tough choice: Go on, 10 miles a day and risk death; turn around; or hunker down until spring.

At Independence Rock, hope and limits intersected, a step at a time. In sweeping ways, that has been America in the 21st century.

Through the years, countless westward travelers gathered here, carving their initials or leaving messages in the rock. You can still see some today.

Independence Rock was one of the most enduring impressions from a 3,500-mile, 10-day driving odyssey that took me from South Dakota to Southern California, and – with a cross-country flight thrown in – another jaunt through swaths of Virginia, Maryland and Pennsylvania.

I can report with confidence that Americans in this summer of 2007 are on the move, as always. Gasoline at $3 a gallon has not seemed to calm the Formula One traffic in California, or the semi-and-RV trains into Reno, Nev., or the seemingly endless trains of natural resources rolling out of Wyoming.

Americans have always seemed happiest getting on down the road. And even in an age of satellites and Google maps, you cannot truly appreciate how spectacularly diverse and larger-than-life and full of inviting possibilities the United States truly is unless you traverse it on the ground.

But, as at Independence Rock, Americans in this summer of ‘07 confront limits.

Southern California is caught in the thralls of an eight-year drought. Governments around Los Angeles are urging people to take shorter showers and swap their lawn sprinklers with government-supplied low-volume tricklers. Hybrid cars have become more commonplace on the roads.

In South Dakota, billowing plumes from ethanol plants attest to the race to wean an economy from imported energy. The days of easy credit and interest-only loans appear to be fading, and the housing market has cooled.

And a war in Iraq that was supposed to unleash a new democracy in a troubled Middle East has turned into a struggle for stability. For this challenge and more, the American political system has struggled to find a way forward.

Like ancestors at Independence Rock, Americans confront another intersection of hope and reality.