North–South Trade and Human Movement Between the Missouri and Saskatchewan River Watersheds Before the Settler Era

 

Drawing of "typical" activities in the life of a Plains Indian band.

Overview

Long before railways or agricultural settlement transformed the northern Great Plains, the watersheds of the Missouri and Saskatchewan rivers were linked by one of the most dynamic and consequential Indigenous trade systems in North America. Goods, people, languages, technologies, and biological realities — horses, disease, seeds — all moved through a corridor stretching roughly 800 kilometres north to south, across what are today the Canadian prairies and the American northern plains. The archaeological record pushes this connectivity back at least 13,000 years, while ethnohistorical and documentary evidence illuminates its richest era between roughly 1650 and 1870, before railways and the settler rush severed the old routes and confined peoples to reserves and reservations.

I. The Physiographic Corridor

The two great watersheds are not isolated: they share a broad geographical ramp across the Missouri Coteau, a narrow band of hummocky glacial upland that stretches from southern Saskatchewan into South Dakota. The Coteau's eastern escarpment and the Souris (Mouse) River basin provided a natural north–south route flanking the Missouri's upper reaches, while the Assiniboine and Qu'Appelle river systems offered branching connections westward into the Saskatchewan basin. Along the western edge of the corridor, the Old North Trail — a corridor worn deeply into the foothills east of the Rocky Mountains — extended from the Arctic to Mexico, and forked near what is now Calgary. Together these physiographic features meant that north–south movement across both watersheds required no ocean or mountain crossing; the terrain actively invited it.[^1][2][^3][4]

II. Deep Prehistory: Stone, Shell, and the Earliest Networks (13,000 BCE – 500 CE)

The archaeological evidence for very long-distance exchange is unambiguous. Researchers have analysed more than 1,200 obsidian artifacts from nearly 100 Alberta sites dating from 13,000 to 300 years ago. Obsidian does not occur naturally in Alberta — every fragment was imported — with the majority sourced to Bear Gulch, Idaho, and Obsidian Cliff, Wyoming, both within or near the upper Missouri watershed. The scale of this movement is remarkable: archaeologist Timothy Allan concluded that "likely millions of people were in contact with one another," and that the scope of the network was "way more massive than we thought".[^5][6]

Knife River Flint (KRF), quarried in Dunn and Mercer Counties of North Dakota near a Missouri tributary, provides another north–south tracer. The KRF quarry complex covers about 200 hectares with 29 pit complexes; the flint was traded north into Alberta and beyond for more than 13,000 years. The trade in KRF has been documented before 2000 BCE, making the Missouri-to-Saskatchewan stone exchange one of the oldest continuously documented commercial relationships on the continent.[^7][8]

Marine goods completed the long-distance picture. Copper from Lake Superior, dentalium shells from the Pacific Northwest, conch shells from the Gulf Coast, and marine shells from the Pacific Ocean all appear archaeologically in Great Plains and Saskatchewan basin sites. Archaeological explorations at The Forks (confluence of the Red and Assiniboine rivers) have produced items originating as far away as Lake Superior and northern Texas in a context dated to 1000 BCE. The Forks itself was already functioning as a provisioning and transit stop on seasonal migration routes between the northern coniferous forests and the southern plains during this period.[^9][10][^11]

III. The Mandan-Hidatsa Hub: The Great Plains Entrepôt

The single most important node in the north–south trade between the Missouri and Saskatchewan watersheds was the cluster of permanent earthlodge villages of the Mandan, Hidatsa, and Arikara peoples along the Missouri River in what is now central North Dakota. As early as 350 CE there existed a highly developed network of trade throughout North America, with these villages serving as primary centres. The Mandan established villages near the Heart River by at least 1450 CE, and the Mandan-Hidatsa complex became known as the "Marketplace of the Central Plains".[^11][9]

What made these villages so central was an agricultural surplus — corn, squash, beans, sunflowers, and tobacco — that could be exchanged with surrounding nomadic peoples for bison products, horses, and exotic goods. Visiting peoples included the Cree, Assiniboine, Cheyenne, Crow, Comanche, Kiowa, Arapaho, and Teton Sioux from every direction. Seasonal trade fairs typically occurred in late summer and early fall when the corn was ripe, with Washington Matthews recording that when the Dakota saw the blazing star blooming on the prairie, "they knew the corn was ripe, and went to the villages of the farming Indians to trade". Goods at these fairs could be compared using a standard of value — the buffalo-horse, a horse fast enough to run down a bison.[^12][13][^14][9]

The Mandan trade network at its height was continental in reach: dentalium shells arrived from the Pacific Northwest, and the villages acted as relay stations through which goods moved between the Missouri basin and the Saskatchewan basin in the north, the Rocky Mountains in the west, and the Missouri Valley in the south and east. Archaeological evidence of copper, Pacific shells, and obsidian at the Knife River villages confirms the physical reality of these recorded exchange relationships.[^15][16][^11]

IV. Key Peoples as Brokers of the North–South Exchange

The Assiniboine (Nakoda)

No people were more central to the north–south corridor than the Assiniboine, who split from the Yanktonai Sioux around 1640 and migrated west into the northern plains. By the early 18th century their territory bridged the two watersheds, straddling what is now southern Saskatchewan in the north and the upper Missouri confluence zone in the south. They traded bison meat and pelts south to the Mandan and Hidatsa, receiving corn, squash, beans, sunflowers, and tobacco in return.[^13][17]

The pivotal role of the Assiniboine as commercial and geographic intermediaries is illustrated most precisely by the 1738 journey of French explorer Pierre La Vérendrye. Operating from posts in Manitoba near Lake Winnipeg, La Vérendrye accompanied an established Assiniboine trading party south through the Turtle Mountains and along the Souris River, reaching a Mandan earthlodge village on December 3, 1738. His party of 52 people included 25 Assiniboine men and women. The Assiniboine had been conducting these journeys regularly long before La Vérendrye joined them — the route was already worn — and from 1770 to 1778 Assiniboine traders routinely carried corn and furs north from Mandan country up the Souris River to the French post of Fort La Reine, though warned by Sioux not to traffic with Europeans.[^18][19][^20]

The Plains Cree

The Plains Cree emerged as major brokers of a different phase of north–south trade after 1670, when they allied initially with the Blackfoot and later with the Mandan to the south. Supplied with European firearms from Hudson's Bay Company posts at the northern end of the exchange chain, the Plains Cree became middlemen sending guns deep into the Blackfoot Confederacy while receiving bison robes, hides, and — crucially — horses in return. The alliance with the Mandan gave the Cree a southern supply of horses as well. This firearms-for-horses circulation, running north to south and south to north simultaneously along the Saskatchewan-Missouri corridor, was one of the most consequential feedback loops in 18th-century Plains history.[^21][22]

The Blackfoot Confederacy

The Blackfoot Confederacy (Siksika, Kainai, Piikani) occupied the western flank of the corridor, their territory stretching from the North Saskatchewan River in the north to the Yellowstone River in Montana. Their engagement in north–south trade was inseparable from the diffusion of the horse. Around 1730 the Blackfoot were attacked by Shoshone on horseback — the first time they had encountered horses, which they named "Elk Dogs". Between 1730 and 1750 they acquired their first horses through peaceful trade with their neighbours the Flathead, Kootenai, and Nez Perce, and by the mid-18th century horses had transformed Blackfoot life and trade capacity entirely. When Anthony Henday of the Hudson's Bay Company travelled inland in 1754 and reached a Blackfoot camp of 322 lodges near present-day Red Deer, Alberta, he found a wealthy people confident enough in their resources — horses and buffalo — to decline his invitation to travel north to York Factory to trade.[^23][24][^25][26][^27]

The Blackfoot's strategic position astride the Old North Trail gave them influence over north–south movement along the foothills corridor. They controlled access to horses for northern peoples and in turn received guns and European goods from Cree and later from HBC and NWC posts on the North Saskatchewan River.[^26][27]

V. The Horse Diffusion as a North–South Trade Event (circa 1680–1760)

The northward spread of the horse was itself the most transformative north-to-south trade movement of the pre-settlement era, and it travelled the same corridors as material goods. Horses reached the northern plains gradually from the southwest after the Pueblo Revolt of 1680 released large numbers of Spanish horses into Indigenous hands in New Mexico. Through a combination of trade and raiding, horses reached present-day southern Alberta by the 1720s. The Plains Cree acquired horses by approximately 1730. The Nakoda (Assiniboine) gained mobility on the plains when they obtained horses, allowing them to range much greater distances in pursuit of buffalo and trade. The cultural transformation was noted immediately by visiting Europeans: by the time Henday encountered the Blackfoot in 1754, horse-mounted bison hunting on a massive scale was already the dominant economy of the corridor.[^24][28][^29][20][^23]

The diffusion was southwest-to-northeast, but it ran through and was mediated by the same Mandan-Hidatsa villages at the Missouri that anchored north–south trade. The Mandan served as relay nodes for horses coming from the south and west and heading north, just as they relayed corn and obsidian in other directions. The Nakoda coached their Cree allies in horse culture as the animals moved northward, completing a chain that linked Mexican plateaus to the Saskatchewan River valley within roughly two generations.[^30][1]

VI. Guns Moving South, Horses Moving North: The 18th-Century Exchange Engine

The dominant dynamic of the 18th-century corridor was a counter-flow: firearms and metal goods moved southward and westward from Hudson's Bay Company and later North West Company posts on the Saskatchewan; horses and agricultural products moved northward and eastward from the Missouri villages and the southern horse-breeding networks. The Cree, operating from positions along the North Saskatchewan River, were essential catalysts. Their alliance with the Mandan gave them access to horses; their access to HBC posts gave them guns to sell or trade. The Assiniboine performed a parallel role in the Souris corridor east of the Coteaux.[^22][21]

This exchange had geopolitical consequences. Peoples who acquired guns and horses faster than their neighbours could project force across the corridor, displacing others. The Cree and Assiniboine alliance pushed the Atsina (Gros Ventre) out of the Saskatchewan valleys through sustained raids across the 18th century. The Blackfoot, once they acquired both horses and guns through the corridor trade, used their dual advantage to dominate a vast territory and nearly exterminate the Shoshone in battles over hunting territory between 1780 and 1805. Epidemics of smallpox, also moving along the same trade routes, reached the Assiniboine along the Souris in 1782 and cut their population dramatically before they recovered enough to resume trading operations by 1784.[^27][20][^21]

VII. The HBC-Mandan Trade: Formal Documentation of the Corridor (1795–1812)

European traders did not create the north–south corridor; they inserted themselves into it. The most direct documentary evidence is the period 1795–1812, when the Hudson's Bay Company formally entered the Mandan trade. On November 12, 1795, HBC employees left Brandon House on the Assiniboine River to travel south to the Mandan villages with North West Company rivals who had already established a trade there. For the next fifteen-odd years, the HBC traded regularly with the Mandan, receiving pelts, provisions, and horses. The NWC had preceded them, and before that, French traders from Montreal had been in the trade as early as La Vérendrye's 1738 journey. The Mandan villages drew Canadian traders, St. Louis traders, and a succession of explorers including Lewis and Clark in 1804, each finding a commercial infrastructure that Indigenous peoples had maintained for centuries.[^31][32][^33][12]

VIII. The Old North Trail: The Western Corridor

Parallel to and west of the river-based exchange was the Old North Trail, which ran north and south along the eastern face of the Rocky Mountains from the Arctic to Mexico. The Blackfoot describe it as originating in the migration of a great tribe from the distant north, worn so deeply by generations of travellers that travois tracks and horse trails were still visible in the early 20th century. The trail forked near present-day Calgary, with one branch extending north into the Barren Lands and the main trail running south through Montana. Tribes using this corridor included the Blackfoot, Cree, Kootenai, Salish, Gros Ventre, Shoshone, and later the Métis. The Old North Trail served as the "backbone" of a trail system used for over 10,000 years, connecting the Saskatchewan basin in the north to the Missouri and beyond in the south.[^34][4][^35][36]

IX. Seasonal Migration and Human Movement

Trade and seasonal movement were inseparable. The north–south corridor was traversed not just by dedicated trading parties but by entire peoples following the bison. The great herds moved seasonally, and bands moved with them, creating regular cycles of contact between peoples from different watershed systems. The Assiniboine, for example, inhabited northwest North Dakota, northeast Montana, and southern Saskatchewan simultaneously and seasonally. Many groups used The Forks (present-day Winnipeg) as a rest stop in seasonal migration routes from northern coniferous forests to the southern plains. The Cree's westward expansion during the early 18th century was itself a sustained population movement through the Saskatchewan watershed toward the Missouri corridor.[^37][10][^38][21]

Inter-marriage was structurally embedded in this mobility. Trading gatherings — whether at the Mandan villages, at Cree meeting points on the Saskatchewan, or at neutral grounds along the Qu'Appelle — were also occasions for diplomatic alliance-making and inter-band marriage. The movement of peoples therefore produced genetic, linguistic, and cultural mixing across the corridor, making the north–south exchange zone a region of continual hybridisation long before the arrival of the Métis as a recognized distinct people.[^39]

X. Disruption and Legacy

The north–south trade system survived — indeed thrived — in the early fur trade era because European traders inserted themselves into existing networks rather than replacing them. The decisive disruptions came in sequence: smallpox epidemics (1781, 1837–38) killed enormous proportions of corridor populations, especially the sedentary Mandan and Hidatsa who were concentrated in villages and therefore most vulnerable to contagion. The drawing of the 49th parallel as an international boundary in 1818 imposed a political line across the corridor's southern Saskatchewan-northern Montana zone that had no precedent in Indigenous geography. The bison herds collapsed by the early 1880s, destroying the economic basis of the nomadic exchange system. And the arrival of the Canadian Pacific Railway in 1883 and the American Northern Pacific in 1881 finally reoriented commerce east–west, along lines of settler agriculture rather than north–south, along lines of bison migration and Indigenous trade.[^31][27]

The peoples of the corridor did not vanish. Assiniboine bands settled on reserves on both sides of the Canada–US border in the 1870s. Blackfoot, Cree, and other nations whose territories had straddled the border for centuries found themselves divided between two states. The trade routes, now overgrown or paved over, persist as ghost infrastructure — visible in the alignment of some modern highways, in the place-names of river crossings, and in the archaeological record of stone tools moving from the Missouri basin to the Saskatchewan basin for more than ten millennia.[^13]

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