Hello all! Sorry I haven’t blogged in awhile. I’ve been so busy trying to complete the maps for this year by the June 30th deadline. But, I am proud to announce that the Geologic Maps for Shirley and Fairfield Bay are now published and available on our website! Click below to view and download the maps.
The process to create these maps takes an entire year. I kept you updated each field week from July to April last year, so I thought you might be interested to know how we take the raw data we collected in the field and use it to make a map. First of all, it’s a collaborative effort. It takes a lot of people who specialize in various disciplines working together to make this product. Basically, drawing the map starts with the notes we took in the field. At each point, we tried to identify the rock formation exposed there. Sometimes this was difficult, especially in the southern portion of the Boston Mountains Plateau where we worked this year. These rocks are all so similar–mostly sandstone and shale. Nevertheless, if you cover as much ground as we did, you begin to discern similarities in the rock types and bedding structures, and can make formation calls based on those similarities. Many of the points are taken on what we considered to be contacts between different formations. These points are used to hand draw contact lines on a blank topographic base map. These lines are continued into areas where the contacts may not be exposed, because we assume lateral continuity of these units. Many times there are topographic breaks along these contacts which can help us draw the lines in areas of poor exposure or in areas we just didn’t get to. Structural lines are drawn along the trace of faults or other structures at the surface in areas where we saw the hallmarks of faulting such as deformation bands and non-vertical joints. Also, the many strike and dip measurements we took were plotted on the map and helped determine orientation of faults and other structures, such as the axis of a monocline. Once all the lines were neatly drawn on the topo, it was scanned into the computer and georeferenced to the grid of all quads in the state. Next, each line was painstakingly digitized in ArcView by one of our cartographers, in this case Brian Kehner. The digitized map was then added to a layout that Danny created in Adobe Illustrator.
The layout includes descriptions of each formation developed from our field notes and are specific to each quad. A correlation of map units, a generalized stratigraphic column, an inset map of the locations of the field points, a symbol chart, and a rose diagram of the frequency of each joint direction are also added to the layout. A cross-section based on formation thickness is hand drawn, digitized, and placed along the bottom of the layout. Formations are symbolized by color and an abbreviation. Sometimes photos are added to balance the layout. Also plotted are any quarries or pits we found or were in the economic commodities database we keep at the Survey.
After we have a reasonably good map, it’s printed and set out for staff review. They really let us have it, but this editing process always greatly improves the maps. After two or three revisions, we finalize it and send it to the USGS by June 30 to fulfill the requirements of the STATEMAP grant. Whew! What a relief! This year, as in years past, I have designed a commemorative STATEMAP t-shirt. I’m taking orders until July 25th if anyone is interested. They are available for the cost of the shirt you choose plus the printing. Please email me at firstname.lastname@example.org for details. Now we get ready to head back out again to our new field area. This year we’ll be mapping the Parma, Prim, and Greers Ferry quads. I’m breaking in a new field partner this time out. Andrew Haner says he’s looking forward to seeing some of the Arkansas wilderness. I just hope the snake count is low this year. From what I’ve see so far, the ticks seem to be at an all time high. I’ll try to keep you posted, but will be out of the office four days a week this year. That will leave little time for blogging. So until my next post, I’ll see you on the outcrop! Richard Hutto