northern Rocky Mountains begin in northwestern Canada
and run down the western coast. To the east of the moun-
tains, the Great Plains begin. Th e northern plains are pocked
with glacial lakes. Th e climate in this region is harsh, with
cool summers and cold, snowy winters. During the last ice
age this region was completely covered with snow and ice.
Historians believe that around 11,500 b.c.e. an ice-free corri-
dor opened in the western part of the region, allowing people
to travel south into what is now the United States. By 10,500
b.c.e. the region was much warmer, and plants and animals
had returned.
Much of northeastern Canada is part of the Canadian
Shield, a region of thin soil on top of bedrock; it consequently
cannot support much agriculture. Th e climate is cold and
snowy, and the land is heavily forested. Hunter-gatherers
lived mainly by hunting the ample wildlife in the region.
Southeastern Canada, including the Appalachians and the
region surrounding the Great Lakes and the Saint Lawrence
River, has more fertile soil and a more hospitable climate than
northern Canada. In ancient times the region was covered
with mixed evergreen and deciduous forests. Th e northern-
most portions of Canada, Baffi n Island, and Greenland all
have Arctic climates with year-round snow and ice. Th e only
people to settle there were those who knew how to survive in
such conditions.
WESTERN NORTH AMERICA
Several mountain ranges run north to south in the Pacifi c
Northwest. Inland from these mountains is a broad plateau
that climbs gradually to the Rocky Mountains. Th e Pacifi c
Ocean just off shore is rich in fi sh and shellfi sh that supported
large communities of ancient humans. Th e region has ample
rainfall, especially on the coast. In ancient times this region
was heavily forested; some of its trees, notably redwoods and
sequoias, were among the largest in the world.
Th e coast of what is now California has historically been
quite dry. Th e climate there was stable from the end of the ice
age until about 2000 b.c.e. and then began cycling through
wet and dry periods characterized by droughts that lasted a
century or more. People began settling in the region around
3000 b.c.e., during a period of good weather and high food
production. When the climate became unpredictable 1000
years later, the people adapted to less productive fi sheries and
forests. Droughts and storms plagued the inhabitants of the
region for the rest of the ancient period.
What is now the southwestern United States is much
warmer and drier than the Pacifi c Northwest. Like the Pacifi c
Northwest several mountain ranges run north to south, par-
alleling the Pacifi c coast; these mountains continue south-
ward to what is now Mexico. Rainfall has always been low,
and much of the region is desert. Ancient farmers had to de-
vise means of maximizing the available water. One strategy
was to maintain family networks in diff erent regions; rainfall
varied from place to place, so households in wet areas could
help others in places where the rains failed. Central Ameri-
can agriculture appeared in this region around 1000 b.c.e.,
brought by people moving north on foot from Mexico. Th e
area that is now Arizona and New Mexico had a rough land-
scape with many mesas and steep-walled canyons created by
water and wind erosion. Th e early people of the area took ad-
vantage of this natural landscape by creating homes called
pueblos in the cliff faces.
Th e Rocky Mountains form the highest mountain chain
in North America. Th e Rockies are high, steep, and cold in
winter, when they could be a nearly impassible obstacle for
people on foot. Many animals lived in the mountains, and
ancient hunters went there for seasonal hunts but then re-
turned to their homes on the plains.
Th e Great Plains are an enormous grassland or prairie
east of the Rocky Mountains stretching from modern Canada
to central Texas. Many animals lived there in ancient times,
including giant herds of bison. Th e climate could be harsh;
summers were very hot, and winters could bring multiple
blizzards and heavy snowfall.EASTERN NORTH AMERICA
Th e Mississippi River has long formed a boundary between
the modern western and eastern United States. It drains the
entire region between the Rocky Mountains and the Appa-
lachians. Th e Mississippi by itself is the second-longest river
in North America. When the length of its tributary the Mis-
souri River is added to it, it becomes by far the longest. All
the major rivers in central North America fl ow into the Mis-
sissippi; they include the Illinois, the Ohio, and the Arkansas
Rivers. Th e Mississippi empties into the Gulf of Mexico in
what is now Louisiana. Th e river has long been a major trans-
portation artery for people with boats; it presents some chal-
lenges for sailors but is fairly easily navigable with primitive
watercraft. Th e river is quite wide, especially in its southern
reaches, and was very diffi cult for ancient people to cross. Th e
river’s width is one reason that Central American agricultur-
al practices and crops did not reach eastern North America
until aft er 1 c.e., long aft er they were common in Mexico and
the Southwest. In ancient times the river fl ooded regularly
and was prone to changing course unexpectedly. Th e river
deposits silt at its mouth; these deposits create the Mississippi
delta, an ever-changing landscape of marsh and extremely
fertile soil.
Th e Great Lakes are fi ve large freshwater lakes on the
border between modern Canada and the United States. Th ey
are connected to one another by narrow rivers, and the east-
ernmost lake, Lake Ontario, drains into the Saint Lawrence
River. Th ese large contiguous waterways allowed ancient peo-
ple to move about the region more quickly than they could
have moved overland. Th e climate in the Great Lakes region
is fairly cold, and some portions of the lakes freeze in win-
ter. Th e lakes themselves attract heavy snow. Th e lakes absorb
heat in the summer, cooling summer temperatures and then
warming autumns as the waters release heat back into the air.
Th e land around the lakes is fertile and good for agriculture.climate and geography: The Americas 265