Thomas Jefferson, Meriwether Lewis, and William Clark were all culturally and intellectually Virginians. As the leading figures in what became the Lewis and Clark Expedition, they were steeped in a colonial legacy that optimistically looked westward in anticipation of exploiting the treasures of an Eden that lay beyond the Allegheny Mountains. In the earliest stages of Chesapeake tidewater settlement, Virginia, like other colonies, had an imperial mentality and vision that encompassed the entire breadth of the continent. During the last half of the eighteenth century Virginia's leaders, as well as those in other colonies, began to consider more practical means to reach Eden beyond the mountains. Virginians, including Jefferson and George Washington, believed that by building canals and improving navigation on the colony's major rivers—the James and the Potomac—they could defeat similar schemes that centered on the Hudson River and New York City. And at its grandest, the Virginia imperial vision also reached out to the Ohio, Mississippi, and Missouri rivers. Jefferson's Notes on the State of Virginia confidently declared that such rivers could extend the reach of an American empire beyond the mountains, perhaps even to the western sea.
Copy and illustration from here. Rivers, Edens, Empires: Lewis & Clark and the Revealing of America Before Lewis & Clark