Summer adventuring season is almost upon us, and that means you could soon be hearing agonized sounds from geologists visiting public attractions of geological interest. It's those informational signs, you see. Some of them are quite informative – only they're not exactly accurate. They can sometimes be more aptly described as mis-informational. This tends to frustrate the geotraveler: responses may include groans, gripes, and rolling eyes. One severely-annoyed earth science aficionado at Summer Lake, Oregon took matters (and a Sharpie) into their own hands, and engaged in a little corrective fieldwork.
Hey, at least the illustration is broadly correct!
Despite the mis-informational sign, Summer Lake is a geologically fascinating place to visit. You just might want to bring a Sharpie in case the correction needs refreshing.
You always need to read these signs with a critical eye. Officials do their best, but often, they're not being vetted by people who know the geology of the area they're installed in. And they can be expensive to replace, so correcting them may not be a priority for cash-strapped entities. So if you want to know the accurate story behind what you're seeing, do try to get your hands on a guide written by earth scientists or writers who know how to do their research.
Sometimes, you're going to go to lovely local parks that don't have guides, but do have some problematic signs. Take Deception Falls near Seattle. It's a fantastically beautiful place full of stately woods and raging rivers, with several awe-inspiring waterfalls. One of the most impressive is the one where the Tye River take a 90° turn through solid rock.
Amazing, isn't it? It just begs you to find out what the heck could possibly have caused such a bizarre natural feature. I mean, rivers can be quite twisty-turny, but they generally don't move at right angles!
It's strange enough that it warranted a lot of effort to build a viewing platform and install a sign.
The sign does its best to help out, bless it, but one of these postulations is plum impossible.
Can you tell which one is definitely not the case?
Maybe it'll help if I tell you what sort of rocks we're dealing with. These are tough igneous rocks of the Cascade mountains. Most of them are massive granitic batholiths, but they're shot through with andesitic dykes. In many places, the flowing water has worn those rocks smooth, showing how strong they are, and how seamlessly the andesite merges with the granitic rock.
This is an area that is filled with faults - the bones of the mountain crack and groan as they're pushed up and up by the subduction zone offshore. And rock weakened by faults is much easier for water to erode.
But if someone happened to bring a Sharpie out there to make corrections, I'd encourage them to choose option 2. Absolutely cross out #1: there's no way the river would cut through that solid rock before rotting away the wood. And, while there are many faults, and #3 is a distinct possibility, I'd put my money on the river eroding a dyke. There are places where it obviously has, all throughout the area, and less evidence for a ramrod-straight fault line darting through.
I guess two out of three ain't bad, eh?
While you're off on outdoor adventures this summer, keep an eye out for obvious errors on the informational signs you encounter. And, if you are so inclined, you can share them with me! I'll leave the comments open below.