A PRELIMINARY BEDROCK GEOLOGIC MAP OF THE SOUTHERN HALF OF THE RILEYVILLE QUADRANGLE IN PAGE AND SHENANDOAH COUNTIES, VIRGINIA

A new 1:24,000 scale geologic map of the Rileyville 7.5 minute quadrangle, northwestern Virginia, is being created with support from the EDMAP and STATEMAP programs of the US Geological Survey. This map focuses on the southern half of the Rileyville quadrangle, which includes portions of Page Valley, Fort Valley, and the Massanutten Mountains. The new map is digitized in ArcGIS from data collected in the field using ArcPad on Xplore tablet PCs.

Current mapping is focused on the southern portion of the Rileyville 7.5 minute quadrangle, ranging from the South Fork of the Shenandoah River to the Massanutten synclinorium. Lithologies include Cambrian carbonates through Devonian clastic rocks. Cambrian and Ordovician carbonates are concentrated in the southeastern region of the map around the South Fork of the Shenandoah River. To the west, Ordovician carbonates transition to Silurian clastic rocks associated with the Massanutten Mountain ridges. Devonian shales are found between the peaks in the cores of the synclines.

Both Page Valley and Fort Valley are dominated by northeast-southwest trending structures associated with the Alleghanian orogeny. These structures included mostly west vergent folds, west-directed thrust faults, and associated joints and veins. In Page Valley, the South Fork of the Shenandoah River is often constrained by jointing or faulting as exhibited by the parallel nature of river meanders. Another significant structural feature is the Massanutten synclinorium. Duplication of a Massanutten Sandstone ridge is seen in the Luray 7.5 minute quadrangle to the south, which appears to project to the northeast into the Rileyville quadrangle. Further work to the north will be necessary in order to complete the geologic map of the Rileyville quadrangle.