Many millions of years ago the area around Calgary was part of a huge sea. During the dinosaur era, this area was warm, and hosted not only dinosaurs but generous vegetation needed to support such huge animals. Over millions of years this vegetation died and settled on the bottom of this sea. As continents shifted, Calgary became part of North America and the sediments were lifted well above sea level. The pressure of deep layers of rock on the decaying vegetation created the vast oil & gas reserves in Alberta today.
The continental drift of the Pacific Plate into and under North America forced the wrinkles in the rock on the western edge of the continent that includes the Rocky Mountains. Several ice ages (the last one was only 10,000 years ago) smoothed the land to the east of the mountains and left behind the fertile western plains that today feed the world.
More history of Calgary