Hot on the heels of a joyful triple post comes the cleaning up phase, śūnyatā.
Let’s start way far back in pre-human geologic time.
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… to the formation of the Rocky Mountains. Apparently that’s a very complicated story. So far, my informant has mentioned the Laramide processes, the Sevier processes, and suggested that the Tetons are something else from those entirely. Does it even make sense to talk about “The Rocky Mountains”?
You’re hitting on one of geology’s great lessons: “Rocky Mountains” is largely a geographic convenience, not a single coherent geological entity. The ranges we group under that name were created by at least three distinct tectonic processes at different times.
The Laramide created the classic Rocky Mountain ranges: the Black Hills, Bighorn Mountains, Colorado Front Range, Wind River Range, and the broad uplifts that define the region.
The Sevier created high ground further west (Nevada through western Montana).
The Tetons are geologically “young” mountains made of very old rock — a classic example of fault-block mountains created by crustal stretching, not the compressional uplifts of the Laramide.
You’ve got Sevier-deformed ranges, Laramide ranges, Basin and Range extensional blocks (like the Tetons), and even ancient Precambrian cores that predate all of this. The Canadian Rockies differ significantly from the Southern Rockies.
Fair enough. My particular interest is in the region of the Continental Divide in Southwestern New Mexico in the vicinity of the Gila Wilderness, and the Sky Island country across the border in Arizona. Are those part of the Rocky Mountains?
No — the Gila Wilderness and the Arizona Sky Islands are not part of the Rocky Mountains, geologically or physiographically. You’ve landed in a completely different tectonic world.
The Southern Rocky Mountains extend into north-central New Mexico — think the Sangre de Cristo range, the Tusas Mountains, the high peaks around Taos and Wheeler Peak. That’s the southern terminus of the Rockies.
Southwestern New Mexico and southeastern Arizona are part of the Basin and Range Province (specifically the Mexican Highland section), which is geologically distinct from the Rockies in almost every way.
The mountains of the Gila Wilderness (the Mogollon Mountains, the Gila Mountains, etc.) are part of the Mogollon-Datil Volcanic Field. If you’re interested in that area, you’re looking at a completely different geological story: caldera collapse, ignimbrite sheets, resurgent doming, and Basin and Range faulting — not Laramide basement uplifts.