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### Surficial geology and geomorphology of Potter County, 
Pennsylvania

#### Professional Paper 288

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#### Abstract

Potter County is located in the Appalachian Plateaus of north-central 
Pennsylvania and contains the headwaters of the Genesee River, the Allegheny 
River, and the Susquehanna River. Drift of Wisconsin age covers the northeastern 
part of the county. This study includes a detailed survev of the surficial 
deposits of the Genesee quadrangle in north-central Potter County and a 
reconnaissance of the remainder of the county; a soil survey and a botanical 
survey were carried on concurrently. The region is a deeply dissected plateau 
having extensive areas of steeply sloping land separated by narrow ridges and 
valleys; there is very little level land. Near the junction of the three 
watersheds the uplands rise to altitudes of more than 2,500 feet. The maximum 
relief in the Susquehanna drainage is more than 1,500 feet; in the Genesee and 
Allegheny drainage it. is about 800 feet. Valley walls are steep (15° to 30°), 
and the uplands have gentle slopes (0.5° to 10°). The drainage pattern is 
trellised. The climate is continental. Temperatures range from about -30° F. to 
more than 100° F. The average annual precipitation ranges approximately from 34 
to 42 inches. Floods may occur at any season of the year. The large volumes of 
water from rain or melting snow carried by small streams come from springs. 
There is little precise data on frost in the ground, but it is probable that the 
ground seldom freezes in forested areas. The soils of Potter County have 
relatively immature profiles with poorly developed horizons that commonly have 
many characteristics inherited from their parent materials. At the great soil 
group level, the zonal soils are divided into Podzol soils and Brown Podzolic 
soils. Many soils have a high silt content in the upper part of the profile, 
apparently derived (at least partly) from a mantle of eolian silt. Mos~ of 
Potter County is covered by second-growth forests consisting of 40- to 
60-year-old hardwood stands. The present forests growing on slopes and summits 
are composed approximately of 25 species of trees. The northern hardwood region 
includes most of the county, with an oak-forest region near the borders, 
principally along its southern margin. Potter County is underlain by sandstone, 
siltstone, shale, conglomerate, and minor amounts of coal and calcareous rock 
that range in age from Late Devonian to Pennsylvanian. These rocks form broad 
open folds that strike northeast. South of the border of the Wisconsin drift, 
and possibly at two localities inside the drift border, are scattered remnants 
of ancient soils (here called paleosol), that were formed in preWisconsin 
time-probably during the Sangamon interglacial stage. This paleosol ranges in 
texture from clay loam to silt loam, ranges in color from yellowish red to red, 
includes a few percent to more than 25 percent of rock fragments, and apparently 
contains a small percentage of gibbsite and varying amounts of kaolinite. Known 
thicknesses range from 1 to 33 feet. Paleosol was developed on diverse kinds of 
parent material, such as till, stratified drift, colluvium, and residuum, at 
altitudes ranging from a few hundred to 2,400 feet. The climatic conditions 
under which the paleosol formed are uncertain; however, these ancient soils may 
record an episode of subtropical climatic conditions during which lateritic 
soils were formed. Perhaps these soils are analogous to the Red-Yellow Podzolic 
soils of southeastern United States. Except for one possible remnant, no 
pre-Wisconsin drift has been recognized in Potter County. The Wisconsin glacial 
deposits of Potter County belong to either the Iowan or Tazewell substages and 
are dominantly till with minor amounts of glaciofluvial deposits. Erratics of 
igneous or metamorphic rock comprise less than 0.1 percent of the total number 
of rock fragments. The till is slightly weathered to depths ranging from 3 to 
about 12 feet. The drift border is indefinite and has been drawn at the southern 
limit of erratics or well-rounded or striated pebbles and is only locally marked 
by a terminal moraine or by a distinct change in the surficial deposits. The 
drift border is relatively straight and crosses the Genesee quadrangle in a 
northwesterly direction with little regard for the major topographic features, 
thus suggesting that the Wisconsin ice sheet had a relatively straight and steep 
front. Over most of the unglaciated part of Potter County, the bedrock is 
concealed beneath rubble that probably was formed during the Iowan or Tazewell 
substage, almost contemporaneously with the adjacent drift. In general, the 
rubble is thickest and most extensive within about 10 miles of the drift border, 
becoming thinner and less continuous farther away. The apparent parallelism 
between a belt of thick periglacial deposits and the drift border suggests that 
the deposits result from climatic factors in operation while the Wisconsin ice 
sheet was nearby. Ancient soil structures or patterned ground occur at, or near, 
the surface of both the periglacial deposits and the adjacent drift. These 
ancient soil structures are so similar to modern forms in arctic or alpine 
environments that they are considered to be the result of vigorous frost action. 
Many of the structures are believed to be a result of down-slope movement of 
debris by solifluction, facilitated by a frozen subsoil as much as 10 feet deep. 
Perennially frozen ground may have been present, but this is not a prerequisite. 
The periglacial deposits underlie long smooth slopes that extend from ridge 
crest to valley bottom. Flood plains are absent near the headwaters of many 
streams, the valley walls forming a V-shaped profile. While frost action was in 
progress, forests probably were restricted to flood plains, lower slopes, and 
scattered upland areas. Large parts of the upland were bare or partly covered by 
tundra vegetation; elsewhere, there were scattered trees but no dense forest. 1 
2 SURFICIAL GEOLOGY AND GEOMORPHOLOGY OF POTTER COUNTY, PENNSYLVANIA Recent 
alluvium and alluvial fans include sand and sandy loams, 1 to 3 feet thick, that 
overlie gravel. The alluvium contains organic matter and lenses of finer 
materials. Thickness ranges from a few to more than 100 feet. Along the 
principal streams the alluvium probably overlies Pleistocene deposits. Most of 
the alluvial fans are composed of unstratified rubbly, pebbly, cobbly. or 
bouldery sandy loams to silty clay loams with local lenses of stratified sand 
and gravel. The alluvial fans mapped in the Genesee quadrangle probably include 
both Wisconsin stage and Recent deposits. The summits of the A.ppalachian 
Plateaus in north-central Pennsylvania have long been recognized as the remnants 
or traces of one or more peneplains. To test this hypothesis, a restored contour 
map was prepared to show the configuration of a supposed peneplain on the 
assumption that the plateau tops are remnants of such an old erosion surface. 
The restored contours delineate a surface that corresponds roughly to rock 
structure. In general, the uplands slope parallel to the dip of the bedrock. The 
major streams, such as the West Branch Susquehanna River, cross the ridges and 
valleys of the restored surface in such a way that it is difficult to suppose 
that the restored surface was ever graded to these streams. On the contrary, it 
is probable that the restored surface never existed and that the plateau tops 
are structurally controlled surfaces held up by sandstone and conglomerate beds 
in the Pottsville and Pocono formations. The plateau tops may have been lowered 
by erosion as much as 200 feet during the Pleistocene-in other words, after the 
major streams were incised. If this portion of the Appalachian Plateaus was ever 
reduced to a peneplain, such a hypothetical surface must have lain many hundreds 
of feet above the uplands of the present day. The only alternative that might 
involve peneplanation is the improbable hypothesis that the plateau tops are 
remnants of a slightly deformed peneplain and that the peneplain was folded 
along the axes of the Appalachian orogeny. This remote possibility is not 
supported by any known evidence. The geomorphic analysis yields no new data on 
the origin of the cross-axial drainage. Regardless of whether the plateaus are 
peneplain remnants or are structurally controlled surfaces, the beginning of the 
major southeastward-flowing streams long antedates the existing landscape. The 
geomorphic history of Potter County begins with an assumed long interval of 
erosion during the Mesozoic and early Cenozoic eras, for which no record remains 
in this area. The southeast master drainage was established by the latter part 
of the Tertiary period (perhaps at a much earlier date), probably as the result 
of the northwestward migration of the Atlanticinterior divide. In late 
Pliocene(?) time, areas adjacent to parts of the West Branch Susquehanna 
River-and probably elsewhere-had a moderate relief ranging from 300 to 700 feet. 
Some segments of the West Branch meandered across a broad valley that lay about 
900 feet above the present streams. The landscape probably was covered by deep 
residual soils, perhaps by saprolite. The early Pleistocene history of Potter 
County is essentially unknown. No deposits of the Kansan stage are known except 
for a possible trace of pre-Illinoian drift on the uplands in central Potter 
County (Ayers Hill quadrangle). Some deposits in central and eastern 
Pennsylvania may be of Kansan age. It is probable that the assumed Aftonian 
regolith was removed by mass movements and other processes during the Kansan 
stage, thus resulting in a lowering of the plateau tops by as much as 10 feet. 
By the close of the Yarmouth(?) interglacial stage the major streams were 
incised to essentially their present depths. The climates of the Yarmouth 
interglacial stage probably produced deep residual soils over the landscape, 
parts of which may still be preserved in the paleosol remnants of the present 
day. No Illinoian drift is known in Potter County, but drift assigned to this 
stage occurs in areas to the northwest and to the southeast. Some valleys, such 
as Kettle Creek valley, were filled with sand and gravel alluvium to depths of 
as much as 150 feet above their present flood plains. It is assumed that the 
Yarmouth residual soils were removed by mass movements and other processes 
induced by a periglacial climate, thus lowering the plateau tops by as much as 
10 feet. During the Sangamon interglacial stage, deep (10-to-20 foot) residual 
soils or paleosol were developed in Potter County and probably throughout much 
of Pennsylvania, perhaps as a result of lateritic weathering in a subtropical 
climate. It is possible that the paleosol was largely removed by mass movements 
and by running water during late Sangamon time. During either the Iowan or 
Tazewell substages of the Wisconsin (perhaps the Iowan), the ice sheet advanced 
into the northeastern part of Potter County. The drift is similar to the Olean 
drift (local usage). The paleosol was almost completely removed by mass 
movements and other processes induced· by a periglacial climate, prior to drift 
deposition. This removal probably resulted in a lowering of the plateau tops by 
as much as 10 feet since Sangamon time. Nearly contemporaneously with drift 
deposition, the periglacial deposits were formed by frost heaving, solifluction, 
and fluvial transport in areas outside the drift border. Soil structures or 
patterned ground were developed on both the drift and the periglacial deposits. 
It is probable that the forests in the periglacial area were greatly restricted 
and that large areas on the uplands were essentially treeless. Little is known 
about the history of Potter County in postOlean time. Presumably, forests 
completely covered the county by the onset of the next substage, during which 
the Binghamton drift of MacClintock and Apfel was deposited. This drift also is 
found in southern New York State. The formation of the alluvium and alluvial 
fans probably began in the Tazewell substage and continued during the Recent 
epoch. Since these deposits were formed there has been very little dissection. 
There is little, if any, difference between soils developed on periglacial 
deposits and soils developed on drift. The roots of fallen trees have disturbed 
the soil horizons, and it is unlikely that the existing soil profiles are more 
than 500 years old. The forested landscape of Potter County has a distinctive 
microrelief ranging from a few inches to a few feet of mounds and pits produced 
by the roots of fallen trees. Most mounds and pits range from 10 to 20 feet in 
length and from 6 to 15 feet in width. On level land, many mounds are oriented 
with their long axes trending northward, and in some areas the orientation is 
random. On slopes, the mounds are oriented with their long axes at right angles 
to the maximum slope as a result of trees falling downslope. The toppling of 
trees increases the permeability of surficial deposits and mixes and destroys 
the soil horizons. The microrelief is a factor in forest development. The 
toppling of trees on slopes is a significant agent of slope erosion. The process 
loosens, breaks up, or overturns the upper 2 to 3 feet of the forest soil, and 
it tends to make the surficial layer more stony and to produce features 
resembling soil structures.

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