The Peak 2 Peak Gondola is a great way to experience the Coast Mountains “close up” from your vantage point 436 metres above Fitzsimmons Creek. One thing that always stands out to me as I gaze out of the gondola window is the incredible geological diversity, a veritable smorgasbord of geology, a patchwork mosaic of different rocks with different origins crammed next to each other in this special place.
Take Whistler and Blackcomb mountains, for example. It only takes 11 minutes to cover the 4.4 kilometres between the two mountains by gondola, but geologically they are worlds apart. Whistler Mountain rocks are relatively young and formed a mere 80 million years ago during the Cretaceous Period. They are a mixture of sedimentary rocks such as shale and silt and volcanic lava rocks such as andesite. Interestingly, this combination of rocks with different erosional properties is one of the reasons we have such awesome, variable and interesting terrain on Whistler Mountain.
In contrast, Blackcomb Mountain is much older, and formed 150 million years ago during the Jurassic Period. During this time, a “pluton” of hot, molten magma slowly moved up through the Earth’s crust before cooling and crystallizing as a solid rock called granodiorite. Keep an eye out for granodiorite; it’s everywhere and makes up about 80 per cent of the Coast Mountains! It is easy to spot—it is coarsely crystalline, hard, and light coloured with flecks of black minerals giving it a distinctive “salt-and-pepper” appearance.
Meanwhile, further up the valley the contrast is even more stark, with the granitic Overlord Massif immediately juxtaposed with ancient sedimentary shale and silt rocks of Fissile Peak deposited 250 million years ago.
The mountains around Whistler are made of hard rocks resistant to erosion, but the rocks underlying the Fitzsimmons Creek valley are not. They are weak and are susceptible to weathering and erosion, geological processes that formed the distinctive steep valley between Whistler and Blackcomb mountains. These rocks are associated with a large “fault,” the Fitzsimmons Range Fault, which runs along the edge of Whistler Mountain passing through Ego Bowl. Movement along this break in the Earth’s crust produced high pressures and temperatures which metamorphosed (altered) the existing valley rocks to produce the weak and crumbly phyllite and schist rocks located below the valley today. I sometimes wonder what it would have looked like if the fault wasn’t there, and there was no valley, just one super large mountain…
The reason there is such diverse geology crammed together in the Whistler area is that the rocks are exotic and were actually formed in different geological settings, hundreds or thousands of km west and south of where they are now. Over time, they were transported by massive oceanic plates like a conveyor belt to the West Coast, until 100 million years ago when they started to “accrete” (stick on) to continental America. More and more rocks piled on behind and created incredible compressive forces. They were then contorted, moved around by faults, forced upwards, and eroded by the elements to form the complex, beautiful, miraculous mountains we can see out of the Peak 2 Peak Gondola today.
Naturespeak is prepared by the Whistler Naturalists. To learn more about Whistler’s natural world, go to whistlernaturalists.ca.