top of page
  • Writer's pictureAmanda

That's the Way the Rockies Crumble

Updated: Feb 16, 2023

Starting a new miniseries, this time about rocks. More specifically, how their form and substance have created some of the dramatic Rocky Mountain landscapes we see today. Starting with sandstone, since some of the Rockies are built from it. Ahh, but not all sandstones are alike. There are fresh, fragile and young sandstones. Others are older, and often harder from past experiences, like this fine grained beauty: its colors and swirls suggest a submerged past, where minerals dissolved, moved, precipitated out, and hardened the cement between sand grains. That past makes for a rock that's darned difficult to break with a hammer, or with ice, water, and roots the way Nature does it. And for the landscape, that means colorful cliff bands that break up a mountain slope. Or for a trail user, those chunks that litter the tread, twisting your ankle or bike wheel, instead of just breaking down into a nice sandy path.

Shale and the Rockies. Part 2 in "That's How the Rockies Crumble". A geologic take on the old saying about cookies and bad luck. But it's a little more predictable with geology, because how the mountains are shaped and reshaped depends on what kind of rock they are made from. In the case of shale--which is evidently the most widespread rock on land--it shatters into thin layers. And they break into smaller pieces at the slightest impact. Not to mention all the surface area on those flaky chips, which means all that exposure to weather. The result is slippery hill slopes covered with delicate rock plates, wafers, and new soil. Which makes for more of a mound than a sharp peak or forbidding cliff. That's one way the Rockies are crumbling, so think about it with more of an open mind next time you find yourself slipping and sliding up that shale talus slope.

Part 3: Here's a brief look at a welded tuff break-up. As you might guess by the name, it's pretty tough in some respects, being made of volcanic ash that was so hot when it landed it all melted together in a glassy matrix. But like glass, it's also pretty easy to fracture. And the fragments are kind of sharp. So what kind of mountains does welded tuff make? Fragile spires, with weather constantly prying off small chunks. Just take a look at the Northern San Juans. There's plenty of welded tuff scattered here and there. Pointy but breakable, like some people I know.!! And don't overlook those fist-sized pieces of it that show up in rock slides and littering the trail. No doubt shattered from some recent painful experience.

Part 4. Now I'm no geologist, but I looked this rock up on Ecosia, the tree-planting alternative to Google, and it seems to be quartz latite. The old geology map actually calls it welded crystal-rich ash-flow tuff of quartz-latitic composition. Translation: welded means melted together, and obviously full of those homogeneous solid substances having natural, geometrically regular forms, with symmetrically arranged planar faces. Ash flow means straight out of the mouth of the volcano, but flowing down it, and tuff is that light, porous rock formed from volcanic ash. Then quartz is of course the hard clear crystal most of us already know. A mouth full of geologic gobbledygook, a mish-mash of contrasting concepts, all make for a messy, crumbly rock. Especially one that's shot through with iron staining from its hydrothermic bath back when Silverton was an active caldera. Brittle, quick to weather, even though it has lots of hard crystals within. It crumbles into a messy mountaintop, but still wondrous, nonetheless!

Part 5 in "That's the Way the Rockies Crumble..." Here's the rock most of us think of when it comes to mountains: rock hard granite. The stuff climbers dream of, and the most durable and beautiful of kitchen counter tops. I was expecting to have a hard time breaking it apart...maybe that quartz vein would be a shear zone. Turns out not so much because it fractured.on the second hit, exposing a rough and grainy face. As it turns out, those interlocking, crystals don't like to break apart that cleanly. Thinking back to granity places like Yosemite or some of the Front Range mountains, where it hasn't been cut, ground, and polished by glaciers, the granite forms pillow-shaped boulders. It crumbles and sloughs off its outer layers, like shedding skin. What kind of mountains does that make for? Rounded peaks, at least that's my hypothesis!

Part 6. What to make of this. As an ecologist by training, I'm all about the connections between things. Even nonliving things like rocks. Never too fond of geology or the chemistry behind it, I'm having to grudgingly admit there's some interesting stuff going on with them as well, because I'm starting to see how they're connected to the other parts of the natural world. It all started on a mountain bike, riding a trail littered with rocks about the size of building blocks. Mile after mile, so annoying, all that bouncing and handlebar twisting. Then it dawned on me: different types of rocks break down differently, making for different types of trail experiences.

Well, if that's the case, I thought, they must make for different looking mountains! And so began my rinky-dink excursion into the world of geology, with a hammer. Clearly, there's a lot that goes into making a mountain--much more than sudden impacts on their constituent rocks. But breaking apart a rock is a start. It reveals a little about how strongly their crystals or grains are cemented together. And maybe something about how the crystals themselves shear. Which inspired me to take a quick peek into the science behind fractures and minerals. Dykes, veins, brittle deformation, joints, shear fractures, wow! it's like opening a Pandora's box of engineering and geoscience! Just enough of a look to see that joints, which form as rocks fracture from stretching, cooling, exfoliating, unloading or swelling with water, are a big part of landscape geomorphology, which includes mountains! Now, slam down the lid on that box; there's way too much there!

After being dealt a healthy dose of humility, I think it's best to approach the subject more circumspectly, perhaps one mountain at a time. Pay attention to the different types of rocks. Notice what the cliffs and rock slides look like. Occasionally try breaking a rock apart. And remember why I'm doing's not to geek out over obscure stuff. It's about having deep understanding and insight into land that I love.


bottom of page