The Bookcliffs at the mouth of Nine Mile Canyon
Roadside geology—standing across the road from an ancient river channel.
I went on a geology field trip yesterday, and I not only learned a lot (and drove everyone crazy with my questions), but I had more fun than I've had for a long time. I'm taking a graduate-level class in sequence stratigraphy. This doesn't mean I know enough to be in the class, just that the prof was kind enough to encourage me to take it.
In front of the ancient channel.
There were only four of us who made it (out of nine students in the class), and two of the four were geology profs. Not a bad learning ratio!
Anyway, there's nothing like a field trip to really see what's going on. We spent the entire morning in the Bookcliffs of Nine Mile Canyon, an area I'd been in a number of times before, but to look at its famous rock art, not its geology. (If you've read some of my earlier posts, you'll recall the Slasher of Nine Mile Canyon.)
Note the abrupt contact between the upper sandstone and the underlying mudstones, indicative of an ancient channel.
We spent some time looking at an ancient river channel, and I realized I'd seen lots of these and didn't know what I was looking at. You may have, too. I learned the indicators that tell you it's an ancient river, some of which are heavier clasts (rocks) at the bottom of the channel grading into finer sediments at the top (just like in today's rivers), and an abrupt contact at its base. River channels are also easy to spot in that they're usually not very wide, so you can walk to either side. We also could see cross-bedding, which told us which way the river was flowing.
We looked at a lot of other stuff, too, which I may write more on later, as we also visited the San Rafael Swell, but I need to go and look at some seismic data for my homework and see if I have a clue of what's going on.
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