BUCKBOARD TO IPAD: A TRIBUTE TO SOUTH MOUNTAIN MAPPERS AND THEIR METHODS

The geologists of Maryland have for over a century been gathering facts in regard to South Mountain. Interpretations have changed and been refined over time as mappers’ technology advances and they build on the work of their predecessors. Maryland Geological Survey’s current digital mapping efforts continue this tradition.

Keith’s 1894 Harpers Ferry folio, drawn on the first generation of USGS topographic maps at 1:125,000, was completed by horse and buckboard. His map established stratigraphic nomenclature and relations that are still in use today. He noted prominent sandstone outcrops on the ridge of South Mountain and drew them as the axis of a syncline thrust over younger rocks to the west.

Fifty years later, aided by cars and recent road cuts, Jonas and Stose’ (1939) and Cloos’ (1941) 1:62,500 maps differed from Keith’s and each other. Jonas and Stose retained Keith’s vision of a syncline and mapped thrust faults bordering both east and west sides. Cloos declared South Mountain the western limb of an overturned anticline, reversed upper and lower ledge forming quartzites described by Jonas and Stose and placed a normal fault west of the mountain.

One hundred years after Keith’s folio, Brezinski (1992) used aerial photography, Landsat imagery and traditional mapping to divide South Mountain’s ridge forming quartzite into three members. The new stratigraphic nomenclature formally captured Jonas and Stose’ two ledge formers and addressed cases of mistaken identity in the middle incompetent unit. Shortly thereafter Southworth and Brezinski (1996) released a map of the 1:24,000 Harpers Ferry quadrangle. Like Keith, they placed thrust faults to the west of South Mountain but had the benefit of structural analysis from a core drilled directly through the fault.

South Mountain is now the test site for Maryland Geological Survey's new digital mapping techniques. Utilizing an iPad, ESRI collector customized for geologic mapping and LIDAR at 1 meter resolution increases mapping accuracy, efficiency and insight.