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.

Image shows a portion of an information sign. To the left is printed matter reading, "Summer Lake was formed by tectonic forces that pushed and twisted this landscape into ridges and valleys over the past ten million years. Winter Ridge, rising to the west of the lake, is Summer Lake's "fault scarp." Millions of years ago, the bedrock of the ridge and the bedrock underlying the lake were pushed together (this is struck through and "pulled apart is written above in black Sharpie). The lakebed sank, and the bedrock split along a north-south fault line, and Winter Ridge rose, forming a steep slope - a scarp - between the two faults." To the right is a diagram of the area with arrows showing the movement of the fault. The arrows clearly show that the two sides pulled in opposite directions, and the center dropped down.
Informational sign at Summer Lake, showing the portion that caused the geo-savvy visitor so much pain. Credit: Dana Hunter

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.

Image shows a waterfall plunging from the right, into whitewater just below. The river flows on along a narrow, straight channel perpendicular to the falls. Dark gray rock and deep green trees rise around it.
The Tye River plunging over a dramatic falls into an even more dramatic right-angle turn. Credit: Dana Hunter

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.

Image shows a sign mounted on the overlook rail at the Tye River. It asks, "Which Way to Flow?" An illustration of a bit of the river occupies the middle. Around it, blurbs say, "Why does the Tye River suddenly turn right in the stretch of river below you? It almost looks as if a thirsty giant bent the channel like a drinking straw. The river probably once ran straight. If you explore the area where it might have flowed, you find an abandoned streambed. Meager rivulets seem from rock cracks, dribbling into a dark, stagnant pool where a waterfall once plunged." To the right are three illustrations and some speculations that will be described in the next photo.
The sign at the Tye River. The left side is fine. The right isn't right. Credit: Dana Hunter

The sign does its best to help out, bless it, but one of these postulations is plum impossible.

Image shows three line drawings with speculations beside them. The first shows a pile of logs stuck in the rocks along the river. Beside it is the first speculation: "No one knows for sure why the river turns. 1. Was the river diverted by the massive stack of logs piled during a flood?" The second illustration is a line drawing of the current falls and course of the river, showing the right-angle turn through granitic rock with mafic dikes. The caption beside it says, "2. Could the water be following a layer of soft rock that runs at right angles to the stream's original course?" The third illustration is a line drawing showing the old channel, the current channel leading to the old one, and the current channel that goes off at a right angle. The illustration shows a rubbly layer in the rock opposite the bend that says "Fault-damaged rock layer." The caption beside it says, "3. Does the stream turn right to flow along a fault line? Fault rocks erode easily since they are cracked and damaged when the earth moves."
One of these things couldn't possibly happen. Credit: Dana Hunter

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.