Southwestern Virginia Case Study

Geologic Map

Elizabeth A. Johnson


This is the map of the area (without annotations):click on the image to enlarge.

Here is an annotated map of the area, showing approximate sample locations and towns, as well as the Fries Fault and major structural units:


Rock Units

Formation Age Sample # Rock Type Protolith
Ashe Formation Protolith Age: 600 Ma (Late Proterozoic). Age of metamorphism: 450-430 Ma. A1 B2, A3 schist Staurolite Schist (Pelite) Fine-grained mudstone
A1 amph, A3 Amph Amphibolite Basalt or Gabbro
UM1 Soapstone / serpentinite Ultramafic (peridotite)
Fries Fault Zone Fault Age To Be Determined A4 Mylonite 1 Mylonite Cranberry Gneiss
A4 Mylonite 2 Mylonite Ultramafic or mafic protolith
Cranberry Gneiss Protolith Age: ~1.1 Ga (billion years) Age of metamorphism: gneissic fabric – 900 Ma? faulting age is unknown. Cranberry Orthogneiss Granite
S5 Cranberry Paragneiss Sedimentary
Striped Rock Granite Crystallization age ~690 Ma. Perhaps associated with Mt Rogers volcanics (~750 Ma)? S6 Striped Rock Granite Not applicable
Unicoi Formation Early Cambrian (like the Chilhowee Group near JMU) Unicoi 1 Shale / mudstone Not applicable
Unicoi 2 Greenstone Basalt
Unicoi 3 Conglomerate Not applicable

Field Bulletin

The map and field descriptions of this area (by Stose and Stose) are available here: 

And from this page (it is free to download, even though it is the DMME “store”):

Like most map bulletins, the text is first, and the maps are at the very end of the .pdf document.

Media Attributions

  • Map from BUL_72 v2
  • Galax map annotated 2


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Introduction to Petrology Copyright © by Elizabeth A. Johnson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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