WHERE THERE IS WATER, THERE IS FOOD

When the massive glaciers that covered the northern half of landmasses across the planet finally withdrew, they released a lot of water at the southern edges.  I don't know what happened elsewhere, but as the glacier's southern edge and the foothills of the Rockies melted, they sent major cascades of water downhill, to the east, digging out the major coulees we see to day.  A huge "crease" in the middle of the midwest guided the incoming water down the Missouri and out the Mississippi to the Gulf of Mexico.  In the mountains the small gathering streams braided together into the major rivers of the East Slope:  St. Mary River, Two Medicine River, Milk River, Birch Creek and Cut Bank Creek.

Roughly along the 49th parallel between the US and Canada, which is a straight surveyed line, is a line of buttes, which were "refugia" when the glaciers came, places where both plants and animals "took refuge".  Even huge earth worms, three feet long and smelling like lilies, managed to survive there.  When President Jefferson bought the Louisiana Purchase, the northern boundary was the edge of the Mississippi/Missouri watershed.  He sent Lewis and Clark to find where that was.  From Cut Bank Creek they could see those buttes plus the glacial till that divided the flow of water between Hudson's Bay in the north and the Gulf of Mexico in the south, so they knew that the 49th parallel rather than the 50th would be the line.

There was an anomaly, which was the St. Mary's valley, dug out by the glaciers.  The Milk River there ran out of the lakes to the north and became Canadian.  For the sake of keeping the boundary straight, the valley was considered American and even diverted some of the water so it ran in Montana south of the border.

But that was much later.  When the ice drew back enough to allow animals to graze, it left shortgrass prairie fed by the snowpack in the Rockies.  Even after the glaciers were gone, enough winter snowfall replenished the run-off to support short grass.  Humans cannot eat grass, though they relished the berries that grew along the streams.  Grass fuels grazers and the key grazing herds of bison were part of the short grass ecology.  Their hooves cutting the dirt crust, their backs digging dusting bowls, their dung manuring the land, were all part of the fitting-together that defines an ecology.  And the buffalo fed the People.

Anthropologists tend to define things according to the artifacts they find, but probably there were People as soon as there were bison.  At first contact they were described as much bigger and healthier people than those who came from the east coast.  Meat is a primary food for predators.  On the East Slope it was augmented by roots, corms and rhizomes, such as those from camas, which were baked in pits.  Berries were dried and so was meat, both pounded together to form "pemmican" a portable rich food.  It was important that summer was hot and dry, since food that was still damp would mildew and be useless.

In the early days the work of killing and processing bison was a communal effort and as much dependent on place as weapons.  The piskun, or steep place that would kill or cripple running animals, was organized at three levels.  First was the feeder meadow behind the bluff or cliff, where smaller groups of bison tended to linger and graze, perhaps give birth.  Second was a rough V of rock piles and branches so that hazers could hide until they jumped up to get the big animals running.  Third, was a place hopefully by a stream -- maybe the one that helped erode the valley -- so that the dead animals could be processed.  

Together the People killed the cripples with stone mauls, skinned and staked out hides to be scraped and treated, and dug pits to fill with stones for fires to cook the fat and marrow out of the bones.  Athabasca Press publishes the excellent description of how one piskun works.  It's by the aptly named Jack Brink.  "Imagining Head-Smashed-In".  http://www.aupress.ca/index.php/books/120137  

When horses and gunpowder finally showed up, quite late in the history of the area, the deepest change was in the practice of hunting bison, because now it could be done by individuals or a small group, breaking up the millennial ties among communities.  Horses became the new commodity while the bison began to diminish.  

Finally, the railroad, an avatar of the Industrial Revolution, changed everything by bringing in non-tribal people, materials for building, settlers who wanted the land.  Also, it became practical to ship out natural resources to the cities back East.  

Until the railroad was finished through the Rockies, the best mode of transportation was the waterways, which is how Lewis and Clark got to the area.  Fort Benton was the town that developed as high up the river as the paddle-wheelers could navigate and it became the first Blackfeet Agency.  As land greed increased, the agency was moved north with rivers serving as the boundaries.  Finally the border settled at the Marias River, while the capitol was built on Willow Creek which feeds into Cut Bank Creek, a new eastern boundary of the reservation.  That edge became important and challenged when oil was discovered in the area.

A. B. Guthrie, Jr., always felt that whoever told the location of Marias Pass to the authorities, so they found the only really viable pass through the Rockies, was betraying the old days because it brought in "civilization."  One of his later novels is organized around the finding of the pass.

"Isaac Stevens’ railroad survey attempted to “discover” the pass in 1854, but failed to find it. In 1889, the Great Northern Railway sent engineer John F. Stevens to locate the pass. Stevens plowed through four feet of snow in subzero weather in search of the 5,214-foot pass, finding it on December 10, 1889. The Great Northern built its line over Marias Pass in 1891. It was not until 1930 that a highway was constructed over it. Before then, motorists on U.S. Highway 2 had to load their automobiles onto railroad cars at East or West Glacier to ship them around the southern boundary of Glacier National Park on the Great Northern." 

https://www.mdt.mt.gov/travinfo/docs/roadsigns/LewisOverthrust.pdf

The Blackfeet, on whose land the pass began, had no concept of its commercial use or how to capitalize on it, but the tourist industry in the rez towns takes advantage of the traffic along Highway 2, which runs east/west just south of the Canadian border.  The early days of Glacier National Park were supported by the tourist towns of East Glacier, St. Marys, and Babb -- heavily advertised by the railroad itself to attract people to the "big hotels" built of timber from the Northwest as was then the epitome of "American Europe" fashion, though the main pictured feature was Blackfeet in parade garb, white buckskin heavily beaded and worn with Sioux eagle-feather headdresses.