More than two centuries ago, President Thomas Jefferson sent a hardy band of explorers on an unparalleled voyage of discovery across uncharted America. Members of the Lewis and Clark expedition were the first U.S. citizens to cross the Continental Divide, the first to reach the Pacific by land, the first to map the landscape that would someday become central to the nation's identity. They also were the last to describe the West before it underwent radical change at the hands of traders, trappers, soldiers and settlers.

As the 2003-2006 bicentennial of the expedition approached, veteran...