1. Geologic Maps Enter

2. Geologic Maps Geologic maps show the areal distribution of rocks of the various geologic ages. Depending on the map scale, it could show all of the rocks belonging to a particular period of geologic time (such as the map on this page) or many different individual rock formations. Other geologic information commonly displayed on geologic maps are the locations of folds, fault traces, and strike and dip measurements.areal distributionmap scalerock formationsfoldsfault tracesstrike and dip measurements Back

3. area Areal refers to the area covered by a rock unit. This becomes a combination of geology (the rock) and geography (the ground surface made up of that rock). In GIS terminology this refers to the spatial distribution of the geologic unit. As you can tell from the geologic map, the areal distribution of the Pennsylvanian Age rock is very large. In fact, almost 75% of West Virginia’s surface is composed of Pennsylvanian Age rocks. In contrast, the areal distribution of the Cambrian age rocks is not only smaller but also segmented due to the different geology of the Eastern Panhandle’s Valley and Ridge Province. The term “areal” should not be confused with “aerial” used to refer to products such as aerial photographs taken by a plane. Areal Distribution Back

4. You are most likely familiar with a highway map. A highway map may have a scale of 1 inch equals 60 miles. If you are driving this means that two towns separated by one inch on the map are actually 60 miles apart. In contrast, this map has a scale close to 1” = 2000 feet. At this scale more detail is revealed because the map covers a much smaller geographic area. The scale of this geologic map is about 1” = 100 miles. At this scale, an overview of the geology of the whole state can be easily seen. Maps such as these provide reconnaissance views of large geographic areas. Map Scale Back

5. More than 200 years ago, a formation was defined as “a distinctive series of strata that originated through the same formative processes”, a definition that is still valid today. Another way to say this is that a formation is a unit of rock that consists of a dominant rock type or has some distinguishing characteristic. Geologists who compile geologic maps think of a formation as a unique identifiable rock unit whose areal distribution can be shown on a map. Two or more formations can be combined into a group where the group has some distinctive characteristics. A visual summary of the major geologic formations and groups of West Virginia is shown in the illustration to the right. These are the names that geologists commonly work with when exploring West Virginia’s geology. Rock Formations and Groups Back

6. Fold axis: Fold axis: The axis of an anticlinal fold is found at the crest of the fold. In a syncline the fold axis is the trough. The trace of the fold axes can be identified by making a geologic map. The red line shows the linear trace of the axis for this anticline. The locations A and B refer to the two limbs or sides of the anticline. Strike & Dip measurements: Strike & Dip measurements: The direction of trend depicted by the fold axis is the strike. Dip (yellow arrow) is the amount of tilt or slope of the limbs relative to the axis. Dip is measured in degrees. In the Low Plateau of West Virginia the dip of the rocks is less than 3 degrees. In the High Plateau the dip becomes a more noticeable 10 degrees in places. In the Valley and Ridge the dip is commonly 25-50 degrees and in some places, like Seneca Rocks, is actually 90 degrees. A B Back

7. Fault Traces: Fault Traces: When the activity of a fault penetrates the surface of the Earth, a fault line or trace is formed. The most famous of these would be the easily followed San Andreas Fault Line in California. The rocks of West Virginia are faulted. Faults are especially prominent in the Valley and Ridge and Great Valley Provinces. However, these are not active like the San Andreas Fault so we do not have earthquakes like California. Most of our faults are geologically very old and were active during the building of the Appalachian Mountains. Much like the axis of an anticline or syncline, fault traces can be observed, measured, and mapped. Demonstrations, using models, have shown that the forces required to make anticlines, synclines, and faults frequently come from directions at right angles to the axial and fault traces. The dominant northeast-southwest orientation of West Virginia faults traces and the similar orientation of our anticlinal and synclinal axial traces is a piece of evidence that indicates that the forces that made the Appalachian Mountains came from the southeast. Back