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Earth Science Week 2020: Geologic Maps

October 18, 2020

Of course, my computer had to misbehave during Earth Science Week. I got behind with my posting, so I’ll try to catch up now.

The 1842 Geologic Map of North Carolina, by Elisha Mitchell. North Carolina was on the cutting edge of science, even then. UNC Geological Sciences is still housed in Mitchell Hall.

Geologic Maps Day is all about the importance of basic geological mapping. What kind of rocks are under your feet? How old are they? Trace elements may be present that are not good for your health? Where are the faults? Are the faults active? What other geological hazards are present?

Geologic Information Systems (GIS) revolutionized the science of Geography. As a senior at UNC in the 1980’s, I thought that Geography was dying. The advent of small computers and GIS software brought it back, healthier than ever. GIS also made Geologic maps more accessible than ever. One place to start is the interactive geologic map. It’s based on the 1985 geologic map of North Carolina, so it’s a bit out of date, but generally correct.

The geologic map you need, for curiosity, for real estate purchases, for development, for research, can likey be found online. There are Google Earth files for each state in .kml format, but these are not necessarily detailed enough for me. The better first place to look is the North Carolina Geological Survey. The first thing you might need to know is the Quadrangle you want. The United State Geological Survey divided the USA into squares of various sizes. You can find the one you want at the NCGS, too: here. Once you have that information, you can find the map you need.

Screenshot of hte USGS Geological Map Datatbase. The “List Pubs in View” button is highlighted on the right.

The United State Geological Survey Geological Map Database is what I use most often. I find the Map View search to be the most useful. (It uses Adobe Flash player, so you may need to give your computer permission to run the plug-in. Also, Flash won’t be supported after December, so who knows what will happen?) You can zoom to the spot you want, hit the button on the right “List Pubs in View,” and you get links to the USGS publication there.

Screenshot of geologic maps of North Carolina, courtesy of the USGS Geologic Maps Database. There’s even maps of the geology under Onlsow Bay, lower right.

The publications and maps can be downloaded in a variety of formats, some of which can be used on your smart phone. When I started in Geology in 1978, I never would have thought that I would be using my cell phone as a combination GPS and GIS device. Google Earth alone would have kept me occupied for days.

Another less obvious way to learn about your geology underfoot: field trip guidebooks. The Carolina Geological Society meets once a year for a fall field trip, and publishes the guidebook and articles on the geology visited. It’s all free to download in pdf format. It’s the single best introduction to your local geology, because you can drive around just like the CGS and visit the sites.

Mountain Press has the Roadside Geology and Geology Underfoot series. These are akin to geologic field trip guidebooks, with mileage logs so you know where you are and what you are looking at. I buy these as gifts for friends heading off on vacation or moving to a new area. Just remember that some states have better outcrops than others.

Finally, Exploring the Geology of the Carolinas: A Field Guide to Favorite Places from Chimney Rock to Charleston, by Kevin G. Stewart and Mary-Russell Roberson. This is a guidebook that mostly sticks to state parks. This is nice for an unexpected reason- in a state park, the outcrops are likely to still be there. I’ve used old field trip guidebooks where the outcrops were bulldozed, or landscaped, or along a railroad track that was no longer there. The science is up to date and the geology and geologic history are well explained, because Kevin Stewart is a professor at UNC Geological Sciences. Go Heels!

So, a few exercises for your curiosity. What are the rocks underneath your home? What fault is closest to you now? If you live on the Coastal Plain, how deep is it to bedrock? Enjoy!

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