114 A HISTORY OF AMERICA IN 100 MAPS
As the previous map reveals, it was the relative
lack of geographical knowledge that led President
Jefferson to sponsor an expedition beyond the
nation’s western boundary to the Pacific Northwest.
In his official request to Congress, Jefferson argued
that such an expedition would clarify the geography
of North America. Like so many before him, he also
sought to advance trade by discovering a Northwest
Passage to the Pacific and Asia beyond. Finally, he
hoped to strengthen the American fur trade relative
to the British by establishing trading posts along
the Mississippi River that would receive goods from
the Missouri and its tributaries. In sum, Jefferson
had several reasons to send Meriwether Lewis and
William Clark up the Missouri River in the spring of
- Two years later, the expedition returned to St.
Louis having traversed more than 7,000 miles. The
information they brought back utterly reshaped the
map of North America.
When they set off, Lewis and Clark knew
comparatively little about the continental interior,
and what they thought they knew was often wrong.
There was no navigable passage to the Pacific Ocean,
nor was there a short portage in the Rocky Mountains
between the headwaters of rivers running east and
west. Rather than a single low, narrow chain of
mountains as depicted on the previous page, Lewis
and Clark found multiple and complex ranges of
much higher elevations. This immediately ended
any hope of an easy overland route. After crossing
the mountains in both directions and from multiple
approaches, the expedition brought back a far wider
picture of the West.
It took more than ten years for the reconnaissance
knowledge gained by Lewis and Clark to circulate.
Once William Clark returned to St. Louis in 1806,
he spent years compiling a map of the expedition
to accompany the publication of his journals. Late
in 1810, the map was redrawn by Samuel Lewis,
who made the map on page 112 as well. Published
in 1814 alongside Clark’s journals, it remains one
of the most important American contributions to
nineteenth-century geography.
AFTER LEWIS AND CLARK
“A Map of Lewis and Clark’s Track,
across the Western Portion of North
America,” copied by Samuel Lewis from
the original drawings of William Clark,
1814
First and foremost, the map captures the extent
of the Columbia River system in the west and the
Missouri River system in the east. The great bend of
the Missouri River was brought into focus, as were
the proper courses of the Clearwater, Columbia, and
Snake rivers. Mountains and valleys were elaborated
in a way that must have awed contemporary viewers.
The expedition also ended the assumption that
western rivers remained wide and navigable near
their headwaters. Instead, Clark described rivers that
were narrow at their source and that broadened as