The geology at Portal 31 is typical of the Breathitt Formation. On the Benham and Appalachia Geologic Quadrangle Map, the coal seam is correlated as the Darby. Another coal seam, the B or Kellioka was also mined in the Portal 31 area see Typical Stratigraphic Section and Coal Seam Correlations. Structure Structurally, Portal 31 lies between Pine Mountain to the northwest and Cumberland Mountain to the southeast, on what is called an overthrust sheet. Pressures from mountain building caused the northeast edge of this block of Devonian, Mississippian, and Pennsylvanian strata to be pushed upward, forming what we call Pine Mountain.
Geologists can trace the amount of movement on the fault.
The northern portion of Pine Mountain has been pushed 4 miles from its original position. The southern edge in Tennessee has been moved 11 miles. As part of the overthrust sheet that moved along with Pine Mountain, the area that is now the city of Lynch was pushed between 4 and 7 miles from where it started.