Ice Free Corridors?

Two glacial ice sheets covered North America during the last glaciation of the Pleistocene.  The "Laurentide" ice sheet extended from the Atlantic seaboard, across the southern shores of the Great Lakes and into Alberta.  In the west a "Cordilleran" ice sheet covered the seaboard mountains in British Columbia and, by 14,500 years ago, extended down the Pacific coast to about 30 miles south of Seattle.

These two glacial ice sheets were periodically joined together stopping migrations of animals and humans through Beringia into southern Canada and the United States.  For at least 10,000 years after 25,000 years ago, great icy barriers would have limited travel between Beringia and North America south of Alaska.

However, at other times during the late Pleistocene, the dates are uncertain, an ice-free corridor was possible through the major river valleys coming from the Rocky Mountains where the "Cordilleran" glacial ice did not meet the western edge of the "Laurentide" glacial ice.

Perhaps the important question is not whether the ice sheets allowed travel from Beringia into Canada and the United States, but whether resources existed in this passage between the ice sheets to support animal and human life.

As on the Bering Land Bridge, the climate in this possible corridor would have been brutally cold and windy; a difficult country even at favorable times of the year.  Blocking passage would be large, biologically sterile, cold meltwater lakes which had formed at the margins of the ice sheets.  This is a landscape so barren that scant vegetation would have supported few animals and therefore very few humans.  The human traveler would have to cross dangerous glacial ice, which even today experienced mountaineers try to avoid.  Boreal forests and forest-tundra, where humans and animals could survive, would have been found much farther south of the Laurentide ice sheet.

Beringian hunters probably had the skills to survive in such hostile environments, but with better food reserves in Beringia there would be little reason for them to travel into this chilly and inhospitable highway between 25,000 and 15,000 years ago.

Emergence of People in North America

Glaciers in North America

During the late Pleistocene the Bering Land Bridge (Beringia) was an important connection between Asia and North America.  Beringia was a large landmass spreading east from Siberia and extending deep into Alaska.  It was the only avenue over which Pleistocene animals, such as the mammoth, could travel between the two continents.

Today Beringia is submerged and we know it as the Bering Sea, a cold and inhospitable arctic domain where remains of ancient plants survive near-perfect in prehistoric muds.  The Bering Strait is locked in ice in winter and hazardous with icebergs in summer.  Only with great difficulty do the Inuit and Aleut peoples live along its shores.

But What Was Beringia Like During the Pleistocene?

Russian and American scientists have learned, by studying the shoreline and taking sea cores of the Bering Sea, that during the Pleistocene Beringia fluctuated at least twice from being a dry landmass as the glaciers spread, which locked up the ocean water, to sea as the glaciers melted.  For two long periods: from 75,000 to 45,000 years ago, and again from 25,000 to 14,000 the Bering land bridge was exposed.

During those thousands of years Beringia was an arid, desolate land with thin snow cover and strong winter winds and storms.  In the spring, rains and melting snowdrifts would change the barren land into a patchwork of vegetation.  Beringia was mainly a treeless land with most plants being very low shrubs.  In the rare more sheltered places alder, dwarf-birch and heath shrubs would be found.  In these sheltered area animals would graze and browse on the available plants.

Possibly the animals would move from one favored location to another throughout the annual growth season of four or five months.  This way fresh food was available from spring until the first late fall snows.  Be careful however, not to think of Beringia as a land teeming with herds of herbivores.  Most likely the animals were scattered throughout the landscape, concentrated at many special sites.  In lowland meadows and near rivers, for example.  Also, not all the mammal species would be in the same place at once.  They would have succeeded one another, feeding at the same locations, but on different plants and in different months.

So what species of animals would have been present in Beringia?  Coming from Asia into Beringia would have been mammoths, bison, caribou, muskox, deer, dire wolves, sabre-tooth cats, dall sheep, saiga antelope, yak, moose, flying squirrels, lynx, lion, dhole, dogs, river otters, ferrets, bears, jaguars, lemmings, mice and voles, fox, rabbits, and wolverines.  Two very important species living in Beringia which had developed in western North America were the horse and camel.  These diverse species, and others not included here, lived in Beringia following seasonal migration routes between Siberia and Alaska.  Remember that Beringia was not an intercontinental highway for these animals.  There was not a deliberate crossing from one continent to another by any animal species.  The Pleistocene mammals lived throughout Beringia and only by chance, following their migration routes, would travel occur between Asia and North America.  Travel farther into North America was blocked periodically by glacial ice sheets which occasionally limited the range of Pleistocene mammals living in Beringia.

What About Human Beings?  Where Do They Fit Into This Place Called Beringia?

By 35,000 years ago humans were moving into Siberia from Europe.  There are two areas in Siberia where archaeological remains of early people are found.  Artifacts of people living in settlements are found in the Lake Baikal region and in the Middle Aldan valley of Siberia.


In the Lake Baikal area the most famous archaeological remains come from Mal'ta on the Angara River.  People lived here between 25,000 and 13,000 years ago in subterranean houses, which were winter dwellings, using animal bones to support a roof made of locked reindeer antlers and covered with hides or sod.  Mal'ta is famous for its ivory carvings of mammoth, women and birds.  Other artifacts from Mal'ta show that the people buried arctic fox after skinning them.  And a child's burial place has also been excavated.

In the Middle Aldan Valley remains of a group of settlements have been found.  At an important site called Dyukhtai Cave the Russian archaeologist, Yuri Mochanov, found mammoth and muskox remains together with spear and arrow points flaked on both surfaces.  Also found were burins, blades, and large stone choppers.  Because the cave had been undisturbed, reliable radiocarbon dates indicated that Dyukhtai had been used by Siberian hunters from 14,000 to 12,000 years ago.  Mochanov argued that these same hunters were the people who had followed mammoth and other big game into North America by 11,000 years ago.  This claim has not been scientifically proved because no other evidence has been excavated through archaeological investigation which would show that the Dyukhtai people did travel across Beringia.

Another argument suggesting that the ancestors of America's native people came out of Siberia comes from Cristy Turner, a scientist studying the physical characteristics of human teeth.  He pores over human teeth and jaws looking for the differences and similarities between the teeth of the Pleistocene Siberian hunters and modern Native American peoples.  He has found that the teeth of the Pleistocene people who lived at Dyukhtai are different from the teeth of the people who traveled across Beringia.  Turner suggests that the Siberian hunters who followed the animals into North America are not the same as those hunter living at Mal'ta and Dyukhtai, but are hunters who lived in northeastern Siberia, closer to Beringia.  Turner thinks that the settlement of North America by these Siberian hunters took place as they traveled through eastern Mongolia and the Upper Lena Basin, across eastern Siberia and from there into Beringia.

Archaeological and anatomical (teeth) evidence shows that possibly several different groups of humans were living and hunting in Siberia during the late Pleistocene and that these various groups of people had the technology to enable them to hunt the animals which migrated across the Beringia.  As yet solid evidence showing which group of Pleistocene hunters crossed Beringia is scant, although it is certain that America's first people did emigrate out of Siberia.

The emigration out of Siberia led the Pleistocene hunters and their families into Alaska and eventually deeper into North and South America.  Over a few thousand years these peoples utilized the animals and plants found in the new land and because the climate did not change appreciably they didn't have to change their cultural habits greatly.  However, over time conditions began to change.

First, the climate of the Pleistocene became drier and warmer as the glacial ice retreated into the Arctic, approximately 10,000 years ago.  Large geographic areas which had been lakes (such as Lake Bonneville) dried up, forests shrank and man of the large Pleistocene animals upon which the people had depended became extinct.  Secondly, the people themselves had become very skilled at hunting the large animals with spears and atlatl.  Possibly, the hunters, by over hunting animal species which were already under stress from a changing climate and habitat, contributed to the extinction of the mammoth, camel, horse and giant ground sloth.  Third, the changing climate also forced the people to find the needed resources at greater distances as plants and animals spread out over greater areas in order to survive.  At 10,000 years ago the people were forced to change their hunting patterns.  After the extinction of the mammoth, camel, horse and sloth they had to hunt fleet running animals like deer, elk, and rabbits.  The people also were forced to leave regions which before 10,000 years had provided enough resources, but after 10,000 years had become dry, desert areas which did not provide sufficient resources.

This changing climate altered the easy simple lifestyle of the hunters and forced the people to experiment with other cultural solutions.  One solution adopted by some tribes was to domesticate plants, such as maize, squashes and beans, and begin to experiment with horticulture.  Horticulture meant living in sedimentary villages and hunting only to supplement the plant crop.  Horticulture meant developing ceremonies to encourage the spirits to provide rain and protect the crops.  Horticulture meant depending on unreliable plants to grow and harvest.   Horticulture meant digging irrigation ditches to supply water from distant areas.  The risks and labor investment involved with horticulture were greater than the risks of hunting.

Geographic Variety of Resources

Naturally the Siberian hunters who crossed into Alaska from Siberia during the Pleistocene did not realize that they had come into a new continent.  Their survival needs remained the same.  What perhaps had changed, as they traveled deeper into North America and South America, was the variety, kinds and concentrations of resource materials as they traveled from one geographic region to another.  It is obvious that each region in America has different plants, animals and rock from which materials can be made.  Consider all of the different regions just in Idaho.  The forests and lakes in the panhandle compared to the desert, basin and range country of southern Idaho.  Each region presented different raw resources to the people which they could use for food, clothing, shelter, tools and weapons.  The common denominator however was technology.  Technology, provides the ability to take raw materials and apply them to a specific use.

Prehistory of Southern Idaho

The earliest undisputed archaeological evidence of human occupation in southern Idaho is from the Wasden Site (also referred to as Owl Cave), located west of Idaho Falls.  The Wasden Site has radiocarbon and obsidian hydration dates averaging approximately 11,000 years ago.  Associated with these dates are stone and bone tool fragments, including fluted projectile points classified as Folsom.  Other evidence for human occupation near the end of the Pleistocene comes from undated contexts, usually surface finds of fluted points all thought to date between 12,000 and 11,000 years ago.  Most notable of these sites is the Simon Site near Fairfield, Idaho that contained numerous Clovis points and associated bifaces.

Desert Dwellers in Idaho

Climates continued to dry and warm after the end of the Pleistocene.  This caused the slow retreat north and east of the long-time residents of southern Idaho leaving the Snake River plain open for neighboring peoples to expand into the area from what is now Nevada. Those groups, who had for millennia been desert dwellers, had acquired the knowledge and technology to take advantage of the wide variety of plant and animals species that thrived in the dry and warm climate of southern Idaho 4,000 years ago.  They exploited deer and antelope along with an occasional bison in conjunction with smaller animals including fish and waterfowl.  It is apparent from the archaeological record that their success in desert areas relied on taking a much wider range of species than their predecessors.

Important sites documenting this changing life way include the previously mentioned Wasden and Simon sites along with Wahmuza, which is located on the Fort Hall Indian Reservation, and Dagger Falls, on the Middle Fork of the Salmon River.  The distinctive style of spear point for this period is the large corner-notched points of the Elko series.

Shoshoni Bow and Arrow. Courtesy of the Idaho Museum of Natural History, Pocatello Idaho

Bows & Arrows & Pots

The desert life way continued up to historic times as the climate cooled into modern times.  Techniques of hunting and preparing food changed as new technology was developed.  The bow-and-arrow was adopted in southern Idaho about 1500 years ago, although the previous spear technology continued to be an important part of hunting and fishing.  Pottery was adopted at about the same time apparently from neighbors to the south in what is now Utah.  Sites such as Wahmuza document the wide variety of species relied upon for food.  At that site, Shoshoni, while in winter encampments, harvested over 60 species of fish, waterfowl, and land mammals.  Evidence from the site shows that deer, pronghorn, bison, trout, ducks and geese were among those species hunted.  Distinctive arrow points, such as the Rosespring corner-notched and Desert side-notched, and pottery are indicative of this time period.