The formation of the Canadian Prairies started with the uplift of the Rocky Mountains near Alberta. The mountains created a rain shadow which resulted in lower precipitation rates downwind.

The parent material of most prairie soil was distributed during the last glacial advance that began about 110,000 years ago. The glaciers expanding southward scraped the landscape, picking up geologic material and leveling the terrain. As the glaciers retreated about 10,000 years ago, they deposited this material in the form of till. Wind-based loess deposits also form an important parent material for prairie soils.

Tallgrass prairie evolved over tens of thousands of years with the disturbances of grazing and fire. Native ungulates such as bison, elk, and white-tailed deer roamed the expansive, diverse grasslands before European colonization of the Americas. For 10,000-20,000 years, native people used fire annually as a tool to assist in hunting, transportation, and safety. Evidence of ignition sources of fire in the tall grass prairie are overwhelmingly human as opposed to lightning. Humans, and grazing animals, were active participants in the process of prairie formation and the establishment of the diversity of graminoid and forbs species. Fire has the effect on prairies of removing trees, clearing dead plant matter, and changing the availability of certain nutrients in the soil from the ash produced. Fire kills the vascular tissue of trees, but not prairie species, as up to 75% (depending on the species) of the total plant biomass is below the soil surface and will re-grow from its deep (upwards of 20 feet ) roots. Without disturbance, trees will encroach on a grassland and cast shade, which suppresses the understory. Prairie and widely spaced oak trees evolved to coexist in the oak savanna ecosystem.

Prairie ecosystems in the United States and Canada are divided into the easternmost tallgrass prairie, the westernmost shortgrass prairie, and the central mixed-grass prairie. Tallgrass prairies receive over 30 inches of rainfall per year, whereas shortgrass prairies are much more arid, receiving only 12 inches or so, and mixed-grass prairies receive intermediate rainfall. Wet, mesic, and dry prairie ecosystems can also form more locally due to soil and terrain characteristics. Wet prairies may form in low-lying areas with poor drainage; dry prairie can be found on uplands or slopes. Dry prairie is the dominant habitat type in the Southern Canadian agricultural and climatic region which is known as Palliser's Triangle. It was once thought to be completely unarable, but is now one of the most important agricultural regions in Canada thanks to advances in irrigation technology.
The dominant plant life in prairies consists of grasses, which may include 40 to 60 different grass species. In addition to grasses, prairies can include over 300 species of flowering plants. The Konza Tallgrass Prairie in Kansas hosts 250 species of native plants and provides habitat for 208 birds, 27 mammals, 25 reptiles, and over 3,000 insects.

Some of the dominant grasses of prairies are Indian grass, big bluestem, side-oats grama, Canada wildrye, and switchgrass.

Prairies are considered to be fire-dependent ecosystems. Regular controlled burning by Native Americans, practices developed through observation of non-anthropogenic fire and its effects, maintained the biodiversity of the prairie, clearing away dead vegetation and preventing trees from shading out the diverse grasses and herbaceous plants. Prairies also depend on the presence of large grazing animals, particularly bison.

Bison are important to the prairie ecosystem because they shape and alter the environment by grazing, trampling areas with their hooves, wallowing, and depositing manure. Bison eat more grass than flowering plants, increasing the diversity of plants in the prairie. Cattle are thought to prefer to eat flowering plants over grasses, but it is not known if that is because of inherent differences in the species or because farmed cattle tend to be confined in smaller areas. Bison dung is a vital source of nutrients for prairie soil, spreads seeds, and supports over 1,000 insect species, including specialist dung beetles which cannot subsist on the feces of any other animal.
In spite of long recurrent droughts and occasional torrential rains, the grasslands of the Great Plains were not subject to great soil erosion. The root systems of native prairie grasses firmly held the soil in place to prevent run-off of soil. When the plant died, the fungi and bacteria returned its nutrients to the soil. These d…

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Nomadic hunting has been the main human activity on the prairies for the majority of the archaeological record. This once included many now-extinct species of megafauna.

After the other extinctions, the main hunted animal on the prairies was the plains bison. Using loud noises and waving large signals, Native peoples would drive bison into fenced pens called buffalo pounds to be killed with bows and arrows or spears, or drive them off a cliff (called a buffalo jump), to kill or injure the bison en masse. The introduction of the horse and the gun greatly expanded the killing power of the plains Natives. That was followed by the policy of indiscriminate killing by European Americans and Canadians for both commercial reasons and to weaken the independence of plains Natives, and caused a dramatic drop in bison numbers from millions to a few hundred in a century's time, and almost caused their extinction.
The very dense soil plagued the first European settlers who were using wooden plows, which were more suitable for loose forest soil. On the prairie, the plows bounced around, and the soil stuck to them. This problem was solved in 1837 by an Illinois blacksmith named John Deere who developed a steel moldboard plow that was stronger and cut the roots, making the fertile soils ready for farming. Former grasslands are now among the most productive agricultural lands on Earth.

The tallgrass prairie has been converted into one of the most intensive crop producing areas in North America. Less than one tenth of one percent (<0.09%) of the original landcover of the tallgrass prairie biome remains. Much of what persists is in cemetery prairies, railroad rights-of-way, or rocky/sandy/hilly places unsuitable for agriculture. States formerly with landcover in native tallgrass prairie including Iowa, Illinois, Minnesota, Wisconsin, Nebraska, and Missouri have become valued for their highly productive soils and are included in the Corn Belt. As an example of this land use intensity, Illinois and Iowa rank 49th and 50th, out of 50 US states, in total uncultivated land remaining.

Drier shortgrass prairies were once used mostly for open-range ranching. With the development of barbed wire in the 1870s and improved irrigation techniques, this region has mostly been converted to cropland and small fenced pastures. In southern Canada, Palliser's Triangle has been changed into one of the most important sources of wheat in the world as a result of improved methods of watering wheat fields (along with the rest of the Southern prairie provinces which also grow wheat, canola and many other grains). Despite those advances in farming technology, the area is still very prone to extended periods of drought, which can be disastrous for the industry if it is signifi…

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