bloody_flapper

Long time lurker, first time poster. Dru- I thought I'd add to the topic because it seems to me that some of the geographic and geologic terminology have been mixed up. I am not a geographer, but a geologist. Did my masters in the North Cascades and a couple of summers of geology in the Selkirks many years ago. You are certainly right that the Canadian Rockies end at the Rocky Mountain trench. However, the Columbias are not similar to the U.S. Rockies. I believe the Canadian Rockies are separated because of their unique provenance in that they are thrusted continental shelf rocks. The U.S. Rockies are generally comprised of continental basement and sedimentary rocks exposed by the Laramide orogony. I believe that would include the Colorado Rockies, the Tetons, Wasatch, Uintas, etc. The Columbias are comprised of allocthonous terranes. That is, they were not originally part of North America but have been 'scraped" onto the continent as the Pacific Plate has subducted beneath the North American Plate. These accreted rocks make up most of Alaska, British Columbia, and extend into Washington, Oregon, Nevada, and California. I think it is still argued where the continental boundary is, but up by you, it is generally considered to be the Rocky Mountain trench. Geologically, the North Cascades are the southern extension of the Coast Plutonic Complex which extends north to Alaska. I guess the Coast Mountains (I always thought it was the Coast Range) is just a geographic distintion separated from the North Cascades by the Fraser River Valley. Feel free to add or correct if I missed something. Cheers ~bf