THE PRE-HISTORIC AND HISTORIC GEOLOGIC IMPACTS OF ICE AND WATER WITHIN THE PA WILDS: A STUDY OF THE SURFICIAL DEPOSITS IN THE RICH VALLEY 7.5-MINUTE QUADRANGLE, CAMERON COUNTY, PENNSYLVANIA

Located within the non-glaciated Salamanca Re-entrant, the headwaters of the Driftwood Branch Sinnemahoning Creek bears two recognizable surficial deposits: periglacial derived boulder-choked hollows, and Holocene-aged alluvium.

In the headwaters of several hollows, large boulders of Pottsville Formation-derived sandstone and conglomerate fill in the ravine bottoms. These boulder fields can be traced straight to the bedrock source on the top of the mountains. Though more thorough geologic mapping is needed to confirm, it appears that in some hollows the Pottsville Formation has been completely eroded away , leaving only the boulders as remnants.

Alluvial cuts along the main valley bottom bear alluvial exposures less than seven feet thick, and water wells commonly show alluvial deposits less than 40 feet. In the main valley bottoms, the alluvium is a moderate yellowish brown to pale brown silt; underlying this silt is a mottled light-olive-gray and grayish orange clayey silt ranging from approximately 0.5 ft to 1.7 ft thick. In the base of the mottled silt horizon, woody debris is commonly observed. Radiocarbon dates from two samples along the Driftwood Branch Sinnemahoning Creek are 605 +/- 15 years BP and 2000 +/- 20 years BP. One sample on North Creek was dated at 1335 +/- 15 years BP. The wide range of ages suggest that the mottled silt lithology is not unique to a single stratigraphic horizon or erosion of older stream deposits upstream allow reworking of woody debris into younger strata. Stream-deposited gravels underlie the mottled silt.

In the headwater streams of Moon Run and Cooks Run, similar-looking mottled silts bear a significantly younger age of 90 +/- 15 years BP. These headwater deposits correlate well with historical logging operations in the county. X-ray diffraction analysis shows the dominant minerals in the mottled silt are quartz and muscovite with minor concentrations of kaolinite, albite, clinochlore, and magnetite.