GRMA Day 5: Day Off

Today may be the least active day of this trip.  I spent a couple hours helping my brother, Jon, install a window that should have taken 20 minutes and did some laundry.  Not much else to report.

The window replacement would have been easy if the replacement window had been the same size as the original, but it was 1/2″ taller so we ripped out the sill, cut the support studs down 1/2 inch, created a new sill and then put the window in. But it finally got done.  Nothing is ever easy.  (That’s been my mantra for years.)

So, lacking any activity to report today, I’ll write briefly about the Rocky Mountains, at least as much as I remember from the scattered reading I did last winter as I prepared for the GRMA.  

The interesting thing about the Rocky Mountains, geologically, is that they’re in the middle of a continent instead of on an edge like the Alps, the Andes, the Pacific Coast Range or the Sierra Nevadas. Even the Himalayan Mountains are on the edge of a continent (Asia) and a subcontinent (India) where two tectonic plates are colliding.  So why did the Rockies rise in the middle of the North American continent?

Although I don’t fully understand the geologic processes the experts painstakingly describe, the answer to the above question seems to lie in the angle at which two tectonic plates under the Pacific Ocean (the Pacific Coast Plate and the Farallon Plate) were subducted under (slid underneath) the North American Plate, whose western edge is just off the coast of North America.  Geologists disagree on why the angle was shallow, but they generally agree that the shallowness caused the uplift to occur more than 1.000 miles from the edge of the plate.  

I took this picture of the northern Canadian Rockies two years ago in Alberta on the way back from Alaska. I’ll be passing by it again in a few weeks.

The uplift generally occurred in an area that had once been a seafloor for hundreds of millions of years and thus had hundreds of feet of sedimentary rock (filled with sea-creature fossils) that served as the peaks of the ancient rockies until much, but not all, had been eroded, leaving the lower level, and harder metamorphic rocks behind.  The Rockies contain all three general types of rock (igneous, metamorphic and sedimentary) and when I point my camera at the gorgeous scenery over the next four weeks, I’ll be photographing rocks created anywhere from more than a billion years ago to several thousand years ago.  If I were to go to the hot springs and mud pots of Yellowstone National Park I would see rocks being created today.  This adventure is going to be a dizzying, colorful, geologic kaleidoscope.

All this tectonic activity occurred during the Laramide Orogeny, about 50 to 85 million years ago.  (Orogeny, I learned, comes from the Greek “oros” [mountain] and “genesis” [creation].  All mountain building events are known to geologists as orogenies.)  During tens of millions of years, as tectonic plates slid under/over one another, the earth’s crust  in the middle of North America buckled and thrust inexorably upward, rising more than 20,000 feet above sea level.  During the next tens of millions of years, ice ages and the glaciers they brought carved and sculpted the mountains and the valleys.  In addition, tens of millions of years of weathering and erosion removed rock from the mountains and filled in the basins between ranges and subranges creating high plains, reducing the height of the mountains by more than a mile.

Geologists have divided large mountain ranges like the Rockies into smaller ranges, subranges and sub-subranges, so if I refer to, for example, the “Bitterroot Range” or the “Sangre de Cristo Range” I’m referring to a range within the larger Rocky Mountain Range.  For a brief time when I’m riding in northern British Columbia I will actually leave the Rockies and spend a day or two in the Pacific Coast Range.

It’s all fascinating stuff, I think, and I would love to take this ride with a geologist, a naturalist and and historian on bikes beside me to help me understand what I’m seeing.  But, I’ll try to stop at the many roadside exhibits, professional displays and museums along the way to fill in the knowledge gaps as best I can.

I’m ready to “rock” and “roll.”  Tomorrow, it’s off to Colorado and the beginning of the Rocky Mountain loop ride.