The Standing Stone: a landslide-emplaced monolith on the North Branch Susquehanna River near Towanda, Pennsylvania

Inners, Jon D. (retired), Fleeger, Gary M., and Delano, Helen L., Pennsylvania Geological Survey, 3240 Schoolhouse Road, Middletown, PA, 17057

The Standing Stone is a gray sandstone monolith that stands erect on the southeast bank of the North Branch Susquehanna River 6 mi southeast of Towanda, Pennsylvania.  First described by an officer of Sullivan’s expedition against the Iroquois in 1779, the stone has given its name to a township on the opposite side of the river, and also marks the northwest boundary of historic French Azilum.  It is situated at the base of a steep, northeast-southwest bluff toward the north end of the “incised-meander reach” of the North Branch on the glaciated, Allegheny Plateau.  Bedrock is mapped as Upper Devonian Lock Haven Formation. 

The stone is at least 25 ft high, 13.5 ft wide, and 4 ft across bedding.  In the immediate vicinity of the Standing Stone are three other large rock slabs lying parallel to the river and leaning against the bank.  The monolith is situated just offshore of a narrow Holocene alluvial terrace that occurs at the base of an extremely steep slope capped by a high sandstone cliff, the top of which lies 330 ft above the river. 

The Standing Stone and the other rock slabs in its vicinity were emplaced by a large landslide involving collapse of a jointed section of cliff directly above.  Weathering and downslope colluviation of a bed of soft, gray shale underlying the sandstone initiated the failure.  The eroded toe of the slide along the river is about 350 ft wide and is now largely covered by the alluvial terrace.  The slide material on the slope between the terrace and the cliff is composed of angular sandstone blocks in a shaly matrix.  Many smaller landslides occur on the adjacent slope and on the surface of the slide itself.  Based on radiocarbon dates on the “16-ft-terrace” from elsewhere on the upper North Branch, the large rock-fall event probably took place between 8000 and 10,000 yrs B.P.

Poster paper presented at the 38th Annual Meeting of the Northeastern Section Geological Society of America, Halifax, Nova Scotia, March 27, 2003.

Reference:

Inners, Jon D., Fleeger, Gary M., and Delano, Helen L., 2003, The Standing Stone: a landslide emplaced monolith on the North Branch Susquehanna River near Towanda, PA: Geological Society of America Abstracts with Programs, v. 35, no. 3, p. 8.

Photo of Standing Stone, Bradford County, Pa.