Subduction leads to Orogeny, or not?

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The group is slowly making their way up towards Missoula, MT and then they will continue almost directly south again so that they end in Oregon instead of Washington. The group wanted to go directly west, but if you look at the map above you'll see that there is a big mountain range right smack in the way. I believe these are the Bitterroot mountains, a part of the northern Rockies. Now the Rockies are a pretty unique mountain range (I know, you could say that about any mountain range), so I wanted to spend some time explaining why the Rockies are here.

First some terminology:
Subduction: This is where one tectonic plate is pushed below another during a collision.
Orogeny: The process of mountain creation.

The Rockies are very different geologically because they are not an active range yet they are still relatively large. Most mountains you can think of lie along tectonic boundaries. The Andes have active volcanism because the oceanic Nazca plate is subducting below the continental South American Plate and these mountains are actively growing. The Himalaya lie along the Indian and Eurasian Plate boundaries and are also active, but they don't have volcanoes because the plates are both continental so there is no subduction. The Alps exist because the African and Eurasian plate collision. The New Zealand mountains, the Californian mountains and Washington coast mountains are from plate collisions and subduction, the Appalachians are from a plate collision millions of years ago (see earlier posts). But the Rockies are right smack in the middle of the continent here and have never been on a plate boundary. So why the heck are they here?

The Rockies were created 70-80 million years ago (they're young!) during a period called the Laramide Orogeny. The cause of this process is still debated, but one of the main theories involves the current activity off the coast of Washington and Oregon. Mt. Saint Helens, Mt. Ranier, Mt. Baker, etc. are active because there is subduction off the coast: The Juan de Fuca plate is being subducted below the North American plate. This has a whole slew of present day hazards (too many for this post), but I think it's interesting because there is lots of history of this plate.

A long time ago, in the Jurassic (so imagine dinosaurs running all around) there was a huge plate roughly where the Pacific ocean is now. This plate was called the Farallon Plate. What remains now of this plate is the Juan De Fuca, the Cocos, and the Nazca Plates.


The rest of the plates has been subducted beneath the continent. So, now there is lots of this plate below the North American Continent.

Many geologists think that some unique sort of subduction led to the Laramide Orogeny. Somehow the Farallon plate subducted normally or at a shallow angle, but it is this plate mass that has pushed up the Rockies. Of course there is more geologic nuance than I can write here and much more than I am even acquainted with. But I think that it is really interesting how the Rockies were created. Of course there have been some changes from the last ice age and subsequent glaciation, but it is essentially the Farallon subduction that has created the mountains that are in the way of the cross country riders as I type.

PS The title is a geology joke. I just thought I'd clarify...