GeoSleuthing 101 – A Mancos Murder Mystery

I have to apologize to the WoGE community for not posting WoGE #60 sooner – it’ll be up in short order as soon as I’ve got this one posted.

The reason for my delay is mainly because it’s been a busy week of teaching. I’m finally getting a break now that it’s Friday afternoon evening. But in a larger sense, the delay stems from the fact that I was really challenged by Active Margin‘s Where on Google Earth #59, so solving it was really satisfying for me – especially when I discovered that it was in a location that I, too, know and love. I figured my fellow WoGEers might appreciate a little insight into how I went about the task, so I’m writing this post to explain the method behind my madness.

Kurtz: Are my methods unsound?
Willard: I don’t see any method at all, sir.

On many Where on Google Earth challenges having a general sense of the geologic feature in question and its orientation will give one a fairly small portion of the world to search. This is especially true for sites with structural features and only slightly less so for features such as rivers and glaciers. I benefit greatly from the use of my SpaceNavigator in solving such challenges because it gives me the ability to scan large areas very efficiently. (If you use Google Earth on a any sort of a regular basis I highly recommend purchasing one!) This advantage is minimized to some degree when the total field of view is down to a few kilometers or less as it has been on a few recent challenges.

I’ll come back to the use of geology in solving WoGE challenges, but first a couple of general strategy tips. One of the obvious ones is to consider the nature of the imagery itself. Because of the patchwork nature and diverse sources of the satellite coverage in Google Earth it is possible to narrow some searches based on the resolution of the imagery and its general hue. I was able to do this, for example in solving WoGE #48 – the Swiss and German imagery has a rather unique green hue to it. (Some of the western US states have similarly distinctive hues.) Very few WoGE challenges span high and low resolution imagery because these seams are generally easy to recognize and tend to disrupt the feature in question, anyhow. (Someday we’re gonna have a real interesting challenge if someone captures imagery for a site and then Google updates the imagery of that site before the challenge is solved.) Another valuable non-geological tool is shadows. Look for them being cast from clouds and/or steep topography. Shadows cast to the east or west only tell you the time of day the imagery was taken (generally not helpful for this sort of challenge) but shadows cast to the north or south can give you important information about the hemisphere in which the imagery was taken. Shadows cast to the north at midday indicate illumination from the south, and thus a northern hemisphere location and vice versa for shadows cast to the south. (Technically you need to know the season to invoke this rule between the Tropics of Capricorn and Cancer, but as a practical matter this rarely comes into play.)

None of this was much help for me on WoGE #59. The area was small, there were no data seams, the hue did not jump out at me (though perhaps it should have in hindsight), and illumination was from the east, so no info on the hemisphere. In a situation like this I actually didn’t spend much time on this challenge in the first day or so after it was posted. That’s partly attributable to the Schott Rule, but also partly because I figure this might just be in someone else’s back yard and as small as the area is I wouldn’t stand a chance if that were the case. When nobody got posted any comments after a day or so, I decided to give it a closer look. The first thing I did was to try to get a sense of the scale of the meander bends and the ridges. Clearly these were not large rivers, so their orientation didn’t mean quite as much – if you look around the region where I ultimately found it you can find similar drainages in many different orientations. Anyhow, the orientation of the rivers was turning out to be a dead end in terms of locating a general region for the imagery.

The next clue I followed up turned out to be more fruitful. There’s absolutely no vegetation in the imagery – something you’d normally see in an image of this resolution and zoom level. Now that immediately gets me thinking about deserts, but it turns out most deserts have more vegetation than this and/or more prominent wind-related features (of which I could detect none in this image). I spent a lot of time searching the Atacama Desert in South America because it was the bleakest (least vegetation) I could think of, but alas – no matches for the hue of the imagery nor the sharpness of the ridgelines. Frustrated, I gave up for another day or two.

On Oct. 8 Jim dropped the hint about the ammonites and inoceramus. Living, as I do, in a former Cretaceous seaway I immediately understood the significance of the age and depositional setting implied by the clue. My first thought was the chalk beds of western Kansas – was it possible this WoGE was in my own backyard? Well, no, because the chalk beds out here have very distinctive bedding, which would be easily recognizable in this sort of high resolution imagery. And then it began to dawn on me… I hadn’t seen any bedding at all! Sometimes the lack of evidence is as important a clue as the one that is covered in oyster shells. What sort of rock would be deposited in an Upper Cretaceous seaway that wouldn’t display obvious bedding? The Mancos Shale! My attention immediately turned to eastern Utah. (In hindsight, the hue of the imagery might have suggested this, as well.) I first searched the area just south of the Book Cliffs in the eastern half of the area of WoGE #7. I found some really promising drainages there, but none that matched the challenge. After that it was a matter of searching for other properly oriented drainages in flat lying Mancos. It didn’t take too long to find my way down toward Caineville, Utah. Bingo!!! Just south of Factory Butte on the east flank of North Caineville Mesa…


The actual WoGE #59 spot is somewhere in the middle ground of the left side of this image. I’ve been though this area as recently as 2005, when I took some of these photos in the area.

Back in my first season of graduate field work (summer 1992) I came through this area for the first time on my way back to Wisconsin from California. My field assistant and I had just spent three days in Escalante, UT waiting for the mechanics to fix a busted water pump and serpentine belt on my Jeep. My field assistant was coming down with walking pneumonia from Valley Fever which he had contracted in California – though we didn’t know that until we finally got him treated at the emergency room in Grand Junction, Colorado (almost makes this a “How the Earth Can Kill You” entry). We stopped for a quick dinner at a little place called the Luna Mesa Cantina (below). On their lunchboard they inform their patrons that the restaurant is located at the Ferron Sandstone member of the Mancos Shale. It is the unvegetated and otherworldly Mancos that gives the Luna Mesa its very fitting name. On learning that we were geologists the proprietor gave us a large selenite crystal from the Mancos as a parting gift. I’ll never forget it. I highly recommend stopping by if you’re ever headed through.


Thanks for the memories, Jim!

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