SMALL SCALE GEOLOGIC MAP OF THE SOUTHWEST PORTION OF OSCAWANA LAKE QUADRANGLE, PUTNAM COUNTY, NY

We mapped the geology of Eden Village Camp, a summer camp located in the southwest corner of the Oscawana Lake Quadrangle in Putnam Valley, NY. The camp is located in the Hudson Highlands. The bedrock of the area is Middle Proterozoic age, approximately 1.3-0.9 billion years old, and formed mainly during the Grenville Orogeny—the last major mountain-building episode during Precambrian time in North America. Since then three major orogenies during the Paleozoic era have metamorphosed and deformed these rocks. The major rock types found in the study area are gneiss and granite.

This area was affected by Pleistocene glaciers which sculpted the landscape and deposited glacial debris including erratics and clayey sediment. Also as part of this project we mapped the boundary between outcrops of Proterozoic bedrock and Quaternary glacial sediment.

The rock units we identified in the study area fit previous descriptions of the Reservoir Gneiss which include granitic and pegmatitic igneous instrusions (Ratcliffe 1992). Because the camp is located between two shear zones in the Ramapo/Dennytown/Canopus fault system, rock units may be allocthonous. Such movement may explain the presence of early Cambrian Poughquag quartzite in the mapped area.

Mapping was done using a Toughbook tablet PC with an embedded GPS receiver and ESRI"s ArcGIS software. We marked the locations of samples taken from outcrops around the 250-acre property and surrounding areas in Clarence Fahnestock State Park as well and constructed a camp map of trails, bedrock and surficial geology.

Future work in the area may include petrographic microscopy to identify mineral assemblages in the Reservoir gneiss, differentiation in the field between glacial striae and fault slickenslides, and provenance studies of heavy minerals in glacial sediments.