Image credit: Screenshot of Opencyclemaps, with notations added by Cujo359
It's a picture of my friend and traveling companion Dana Hunter, doing what she often does on our trips, deciding where she's going to break off another chunk of rock from another cliff face somewhere. That picture won't be included in the print version of the article Dana wrote, though it is in the online version. Leaving it out was one of those editorial decisions that have to be made.
This particular cliff face is alongside Oregon Route 140 in southern Oregon, not far from the Nevada border. According to this hangliding site, which is the most informative one I could find, it's known as Doherty Slide on the Cuano Rim, overlooking the lovely Guano Valley. We were roughly where the "Doherty" in the "Doherty Slide" label is on the map, alongside the road.
If I have my bearings right, Beaty's Butte isn't far from where we were. Incidentally, that region is part of the basin and range formations that exist pretty much from the east side of the Cascades all the way to Colorado and West Texas. It's mostly flat valleys, or basins, bounded by ridges or mountain ranges. The Guano Valley is just one such basin. As you can see from the map (click on it to enlarge, the valley itself is very flat. Much of it south of the highway is cropland, in fact.
Note to whoever named that valley - things don't always sound exotic when they're in a foreign language. I know about fifty words of spanish, and "guano" is one of them. It's not a terribly exotic substance.
The picture that will be published, along with Dana's article, is at the bottom of that article, and it's a pretty good one, too. What I like about both photos is that, in addition to being sights I saw quite a bit of on that trip, they capture people in the act of doing something they find fun and fascinating. Heck, I could have been breaking rocks right there with them, but if the rocks aren't shiny and colorful I don't see much reason to carry them home. If I'd been able to take home twenty or so cubic meters of it, then that would have been useful. That stuff near the top of the photo would have made a splendid rock wall. But little chunks of stuff that will one day be dirt, not so interesting.
What I like about the picture at the top of this article, though, besides all that other stuff, is that it captures something of the magnitude of the task, and the magnitude of the forces that created that task. Compared to all that rock, Dana looks small, and looks as though she's being presented with far too much to do. So much rock, so little time.
But the other meaning is in how those rocks get there in the first place. Here's what I get out of looking at this picture.
There's what looks to be a layer of sedimentary rock (see NOTE 1) at the top of the picture, maybe two. It's several yards (or meters) thick. Whatever laid it down probably happened recently, and was probably very big, because what's underneath it looks to be fairly young as well. Odds are, it was titanic explosions like the one that created Crater Lake, or perhaps it was left there by glaciers. Either way, that was a time you definitely didn't want to be a resident of that area.
Underneath it, right at the level Dana is standing, looks to be either breccia basalt or rhyolite. We found some of the latter at a road cut further down that highway. Either way, big honkin' volcanic doings created it.
Curiously, DoE didn't note the position of the Guano Valley, either.
Image credit: U.S. Department of Energy/Wikipedia, with annotation by Cujo359
Speaking of big honkin' volcanic doings, what's underneath it is even more fascinating. It's basalt in its more solid form, which probably is from one of the volcanic floods that happened a 17 to 14 million of years ago in this region. These were big volcanic floods. It is quite probably one of the Columbia River Basalt Group of basalt floods, which covered substantial portions of Oregon and Washington. That's right, at one time there was molten rock here that could cover a state. You'll also note that just the part you can see is roughly six feet (two meters) thick. There was lots more where that came from, too:
17 million years ago across much of Eastern Oregon, fissures in the Earth's crust erupted staggering amounts of basaltic magma inundating much of the Pacific Northwest beneath successive flows hundreds of feet deep. Coinciding with the advent of Yellowstone Volcanics in Western Idaho these basalt "floods" continued for several million years on and off from vents around Steens and Pueblo Mountains. In present day, signs of these flood basalts can be found along the rangetops of Southeast Oregon, especially along Abert Rim and the east face of Steens Mountain, both of which are nearly entirely comprised of flood basalts stacked one layer upon another. Steens Basalt erupting from vents near Pueblo Mountain left layers of basalt stacked up over 3000 feet thick in places along the Steens Mountain uplift. Great examples of a flood basalt vents can be found in the canyons of Steens Mountain as streaks of vertical basalt cutting through horizontal layers. Other vertical dikes can also be seen across the region, including the Big Fish Fin which can be seen from the summit of Beatys Butte. This impressive basalt feature has been revealed by the gradual erosion of surrounding terrain leaving only the hardened vertical basalt standing.It gets even better, as Wikipedia mentions:
Southeast Oregon Basin and Range
Prior to 17.5 million years ago, the Western Cascade Stratovolcanoes erupted with periodic regularity for over 20 million years, even as they do today. An abrupt transition to shield volcanic flooding took place in the mid-Miocene. The flows can be divided into three major categories: The Steens Basalt, Grande Ronde Basalt, the Wanapum Basalt, and the Saddle Mountains Basalt. The various lava flows have been dated by radiometric dating—particularly through measurement of the ratios of isotopes of potassium to argon. The Columbia River flood basalt province comprises more than 300 individual basalt lava flows that have an average volume of 500–600 km3.I used to think this was one of the safest places in the world, provided you could survive the four months of overcast and flash flooding we call winter without losing your mind. There are no hurricanes here, and no tornadoes worthy of the name. It's just that every thousand years or so, one volcano or or another will make a hundred mile square area uninhabitable, or we have 9.0 earthquake. Some smaller volcanoes, and some smaller earthquakes, happen every century or so. Then every twenty million years or so the earth splits open and spews enough lava to cover a state.
Wikipedia: Columbia River Basalt Group: Transition to flood volcanism
Breaking rocks isn't all that interesting, but how those rocks got there certainly is. I suggest that the next time some libertarian or other deluded person talks about how the government shouldn't be worrying about disasters like this that you ask him where he thinks the lava will go next time, because even though it says every twenty million years and that makes the next one 2.5 million years from now, these things don't run like clockwork. They happen when they're ready.
So yes, I'm being published, kind of. Actually, Dana's being published, and one of my pictures is being published along with it. It's the first time for both of us, and her work certainly deserves it. Still, I'm a bit sorry this photo didn't make it in. There's a lot of story in it, if you think about it a little.
Afterword: I should probably point out, for the record, that I am supremely unqualified to tell anyone what a particular bit of rock is. I'm not a geologist, nor am I particularly well informed for a layman. But what I wrote about how rocks in the region have been formed is true. If it wasn't those particular rocks, then some other rocks on that rim wall certainly were formed that way.
UPDATE/NOTE 1 (Jan. 1): Dana reminds me that these may well be volcanic rocks, too. She and Lockwood Dewitt had both mentioned that similar looking rocks elsewhere were, in fact, volcanic in origin. Because they cool from the top down, their crystals can form in a plane roughly parallel with the ground, which makes them look like sedimentary rock to the untrained eye.
Did I mention I'm not an expert in rock identification?
No comments:
Post a Comment