A NATION REALIZED 115they flowed circuitously toward the Pacific Ocean
or the Mississippi River.
Clark’s map was not without errors, of course.
Because the expedition did not venture south, the
depiction of the Southern Rockies remained vague
at best. Moreover, like his contemporaries, Clark
believed that the headwaters of some of the great
western rivers—the Colorado, the Rio Grande, the Big
Horn, and the Yellowstone—converged. And yet these
limitations detract little from Clark’s achievement in
drawing a far more complex picture of the American
Northwest, one that would remain authoritative until
the expeditions of John Fremont and Charles Wilkes
in the 1840s. Equally important is the way that the
expedition—and its map—drew attention to the West
as a region of its own rather than a pathway to Asia. In
their voluminous notes, Lewis and Clark detailed the
West’s Indian populations, resources, and potential
for settlement. In this sense, Jefferson’s venture was
eminently successful: though it definitively ended the
search for a Northwest Passage, it opened an era of
exploration on the continent itself.