It’s hard to look at the peaks that tower above Squamish and imagine that some of them were once underwater. The mountains we hike, bike, ski, and fly over has been in the making for almost a quarter of a billion years and were conceived at 25km below the Earth’s surface or, even more fantastic, parts of lush islands dragged to the BC coast by tectonic activity.
The compression that built the original Coast Mountains ended about 45 million years ago. For the next 40 million years they sat quiet and eroded back to being a low chain of gentle hills before the next mountain building phase began that created the landscape we know today.
In the present day, the tallest peak in the Coast Mountains of BC is Mount Waddington standing at 4,019 meters. But 10 million years ago the Coast Mountains were so small they didn’t even cast a rain shadow behind them and the interior of BC was lush vegetation.
The greatest volcanic activity in the Garibaldi Provincial Park region occurred while most of the surrounding land was covered in the vast ice sheets of the last glacial age. Garibaldi peak rose quickly through the surrounding ice in a series of eruptions and soon became a gently sloping cone of fragmented lava.
While most of the cone rose clear above the ice, to the west its flank significantly overlapped the glacier and as the supporting ice melted away, the mountain’s entire west face–about 3 cubic kilometres of rock–collapsed in to the Cheekeye Valley below.
In the volcano’s last stage of activity, lava flowed gently out of a vent to the north of the previous plug and formed the now sightly higher northern summit.
Many separate but coalescing igneous intrusions rose up in a succession of pulses from 170 to 50 million years ago, creating the Coast Mountains Batholith, one of the largest bodies of granite and granitoid rock on the planet.
The Stawamus Chief (also known as The Chief) is the giant 710 meter-high monolith that looms over Highway 99 and downtown Squamish. Carved in granodiorite that cooled beneath the ceiling of the early Coast Mountains, The Chief is the second-largest granite monolith in the world.
Mount Tantalus is the highest mountain in the Tantalus Provincial Park at 2608 metres. The origin of the name Tantalus comes from Greek mythology. Tantalus was a Greek mythological figure famous for his eternal punishment in Tartarus. He was made to stand in a pool of water beneath a fruit tree with low branches, the fruit ever eluding his grasp and the water always receding before he could take a drink.
The southern Coast Mountains and the North Cascades contain some of the most perplexing geology to be found anywhere in the province. Instead of a few big terranes, they are made up of a structural stack of little ones.
It seems that these geological anomalies were created in the Jurassic and the mid-Cretaceous period when a plate charging south (instead of north) dragged with it island arcs not related to the North American continent. Eventually the plate, and the islands it brought with it, collided with what is now the coast of British Columbia creating the base for the Coast Mountains.
It is conceivable that Fissile (formally called Red Mountain) got its name from the geological term “fissility”, the geological process by which slate is divided into thin sheets of uniform thickness.
The shale that makes up Fissile mountain was born around 230 million years ago during the Triassic period in an underwater basin between the continent and the terrane (islands off the coast of the main continent).
Anderson, James. D (2011) British Columbia’s Magnificent Parks: The First 100 Years, Harbour Publishing Co. Ltd
Cannings, R & Cannings, S (2015) British Columbia: Natural History of Its Origins, Ecology, and Diversity With A New Look At Climate Change