LANDSLIDING IN 

ALLEGHENY COUNTY, 

PENNSYLVANIA 

PREPARED IN COOPERATION WITH THE APPALACHIAN REGIONAL COMMISSION 

GEOlOGICAl SURVEY CIRCULAR 728 

Landsliding in Allegheny 

County, Pennsylvania 

By Reginald P. Briggs1 John S. Pomeroy 

and William E. D~avies 

GEOLOGICAL SURVEY CIRCULAR 728 

Prepared in cooperation with 

the Appalachian Regional Commission 

To accompany Map of Susceptibility to 

Landsliding, Allegheny County, Pennsylvania: 

U.S. Geological Survey Miscellaneous Field 

Studies Map MF-6858. 

1975 
United States Department of the Interior 

THOMAS 5. KLEPPE, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Library of Congress Cataloging in Publication Data 

Briggs, Reginald Peter, 1929-

Landsliding in Allegheny County, Pennsylvania. 

(Geological Survey circular; 728) To accompany map of susceptibility to 

landsliding, Allegheny County, Pennsylvania: U.S. Geological Survey 

miscellaneous field studies map MF-685.B. 

Bibliography: p. 

Supt. of docs. no.: I 19.4/2:728 

1. Landslides--Pennsylvania--Allegheny Co. I. Pomeroy, JohnS., 1929- joint 

author. II. Davies, William E., 1917- joint author. III. Appalachian 

Regional Commission. IV. Title. V. Series: United States. Geological 

Survey. Circular; 728. 

QE75.C5 no. 728 [QE599.U5] 557.3 08s [551.3' 5' 3] 75-35786 

Free on application to Branch of Distribution, U.S. Geological Survey, 

1200 South Eads Street, Arlington, VA 22202. 
FIGUltE 

CONTENTS 

Abstract 

Introduction 

Recommendations and advice for the nontechnical reader ----------------------

Actions to be avoided or to be taken only with caution --------------------

What the buyer, builder, or homeowner should look for -------------------

Geologic factors affecting susceptibility to landsliding in Allegheny County -----

Selected landslide localities --------------- _ --------------------------------

Glossary ----------------------------------------------------------------

References cited ---------------------------------------------------------

ILLUSTRATIONS 

Page 

1 

1 

2 

3 

5 

8 

11 

16 

18 

1. Location of Allegheny County ___ --------------------------------------------------

2-7. Diagrams showing: 

Page 

1 

2. Landslide nomenclature ------------------------------------------- _ ------- _ 2 

3. Slump -------------------------------------------------------------------- 2 

4. Earthfiow ----------------------------------------------------------------- 2 

5. Rockfall ------------------------------------------------------------------ 3 

6. Debris slide --------------------------------------------------------------- 3 

7. Creep -------------------------------------------------------------------- 3 

8-13. Photographs of: 

8. Landslide largely in fill, Lawnwood Avenue ---------------------------------- 4 

9. Earthfiow on West Smithfield Road ------------------------------------------ 5 

10. Landslide on Painters Run -------------------------------------------------- 6 

11. Landslide in Glenfield area -------------------------------------------------- 7 

12. Pipeline path, Fallen Timber Run ------------------------------------------- 8 

13. Slumped area, Interstate 79 ------------------------------------------------- 9 

14. Map showing selected landslide localities --------------------------------------------- 12 

15-17. Photographs of: 

15. Distressed concrete retaining wall, Baldwin Road ----------------------------- 13 

16. Toe of landslide, Kilbuck Drive -------------------------------------------- 14 

17. Landslide on Lawnwood Avenue -------------------------------------------- 15 

III 

Landsliding in Allegheny County, Pennsylvania 

By Reginald P. Briggs, JohnS. Pomeroy, and William E. Davies 

ABSTRACT 

Man should proceed with caution if modifications such 

as loading, excavation, or changes of the water regime 

are contemplated for slopes in Allegheny County, especially those slopes described on the map as highly sensitive to disturbance by man. Features indjcative of unstable slope conditions include: cracks in buildings, yard 

walls, and pools; doors and windows that jam; fences 

and other linear features bowed out of line; tilted trees 

and utility poles; cracks and steplike ground features; 

hummocky ground; and water seeps. Geologic factors related to the landsliding process include rock types, layering, fracturing, and attitude; nature of soil cover; permeability of rocks and soils; and steepness of slope. 

INTRODUCTION 

Most scientific and technical workers familiar 

with slope-stability proble~ms in Allegheny 

County (fig. 1) agree that man's modification of 

sensitive slopes causes more than 90 percent of 

the landsliding in the area. If man ·causes landslides, he also can control or prevent them, actively by engineering or passively by judicious 

land use. 

A recent study of the county was made to define areas where a significant degree of susceptiFIGURE !.-County outline map of Pennsylvania showing lacation of Allegheny County (shaded). 

1 

bility to landsliding can be expected and thus 

where special engineering attention or land-use 

control are most needed. This report chiefly is a 

supplement to the map by Pomeroy and Davies 

(1975), which is referred to herein as the conlpanion map. 

The report has two chief parts: (1)' A discussion of landsliding causes and evidences of landsliding and (2) a discussion of geologic factors 

affecting landsliding, including brief descriptions of specific landslides. The geographic focus 

is Allegheny County, but advice and dir~ussion 

also have application to adjacent parts of the 

Appalachian Plateaus. 

The report and companion map were prepared 

as part of a larger program sponsored by the 

Appalachian Regional Commission, a r~ogram 

chiefly aimed at improved management of land 

resources in Allegheny County. In addition, the 

report and companion map are contributions to 

a U.S. Geological Survey environmental analysis 

of the Greater Pittsburgh region. 

The writers benefitted from information and 

assistance freely given by many per;;-ons in 

County, State, and Federal governments and 

private firms. They are too many to cite individually, but their help is gratefully acknowledged. In addition, valuable information was obtained from previous reports on landsliding and 

related factors by Ackenheil (1954), Ackenheil 

and Associates (1968), Briggs (1974), Craft 

(1974), Fisher and others (1968), Gray Un 

Wagner and others, 1970, p. 103-105), Hamel 

(1970, 1972), Ham~el and Flint (1969; 1972), 

Kelley (1971), Myers (1935), Philbrick (1959, 

1960), U.S. Soil Conservation Service (1973a, 

b), and Winters (1972). 
RECOMMENDATIONS AND ADVICE FOR 

THE NONTECHNICAL READER 

Landslides affect many Allegheny County 

residents, in some places sporadically, and in 

others more or less constantly. Sometimes they 

pose a severe financial threat or they may be a 

minor but almost constant nuisance. 

Figure 2 shows the general form of many 

landslides and gives nomenclature commonly 

used. Slump (fig. 3) is the prevalent type of 

landslide in Allegheny County. All prehistoric 

and many recent landslide deposits are largely 

the result of slumping. Earthflows (fig. 4) are 

common, and rockfalls (fig. 5) and debris slides 

(fig. 6) are rather frequent, particularly from 

highway and railroad cuts. 

Most landslide~s actually are composites of 

two or more of these types, but usually a given 

landslide is labelled for the dominant type present. For example, a large slump may have rockfalls and debris slides a.t its head, and earthflows may occur at its base. 

Rockfalls are the most rapid landslides, ranging in duration from a split second to a few 

seconds at most. Debris slides normally last 

from seconds to minutes, but if the source of 

debris is large, for example, a huge mine-refuse 

bank, a debris slide can move more or less continuously for hours. Duration of an earthflow 

depends largely on its size. Smaller earthflows 

can be finished in minute~s, but most probably 

last for an hour or more. Slumps commonly 

move relatively slowly, forming in hours or 

even months; some slumps, however, can take 

place in minutes. 

Soil creep is a gradual, more or less continuFIGURE 2.-Nomenclature of parts of a landslide (simplified from Eckel, 1958). 

2 

ous downslope movement of soil (fig. 7), and 

usually is not considered a landslide process, but 

it can be accelerated into landsliding. The basic 

distinction is that an area of cr~~ep does not 

show significant ground I?reakage--no scarps or 

cracks. 

Generally landslides in the county are slowmoving so there is ample time to avoid personal 

hazard; deaths and injuries are r~.re. Rockfalls 

are the chief exception. In one place in adjacent 

Beaver County in 1942, 150 cubic yards of rock 

FIGURE 3.-Slump--coherent or intact masses that move 

downslope by rotational slip on surfacr~s that underlie 

and penetrate the landslide deposit (from Nilsen, 

1972). 

FIGURE 4.-Earthflow-colluvial or fill materials that 

move downslope as a viscous fluid, for example, thick 

syrup (from Nilsen, 1972). 
Fallen sandstone block 

FIGURE 5.-Rockfall-rock masses that move primarily 

by falling through air (from Pomeroy, 1974). 

FIGURE 6.-Debris slide--incoherent or broken masses of 

rock and other debris that move downslope by sliding 

on a surface that underlies the deposit (from Nilsen, 

1972). 

fell and crushed a bus, killing 22 passengers and 

injuring four (Ackenheil, 1954) . 

Property damage ranges from very serious in 

relatively rare cases, such as the destruction of 

a dwelling, blockage of a transportation route, 

and destruction of a reservoir, to minor in very 

frequent cases, such as slumping at the edge of 

a lawn or highway shoulder. Thus few individual landslide events are extremely costly, although the Allegheny County Department of 

3 

FIGURE 7.-Creep-Common evidence: (A) moved blocks 

of rock; (B) trees tilted at appreciable angles downslope with curved trunks concave upslope; (C) displaced posts, poles, and monuments; (D) broken or 

displaced retaining walls and foundations; (E) roads 

and railroads moved out of alinement; (F) turf rolls 

occurring downslope from creeping boulders; (G) 

stone line near base of creeping soil (modified from 

Sharpe, 1938). 

Planning and Development has estimated costs 

of damages from landsliding in the county from 

1970 to 197 4 at nearly 2 million dollars each 

year (W. C. Morrison, oral commun., 1974). 

Doubtless unreported, and so not included in 

this figure, are many events that may cost the 

individual homeowner perhaps 100 dollars for 

repair. 

ACTIONS TO BE AVOIDED OR TO BE TAKEN 

ONLY WITH CAUTION 

Most landslides in Allegheny County result 

from loading the tops or cutting into sensitive 

slopes, construction of fills on slopes, or altering 

water conditions of slopes. No significant actions should be taken without site investigations 

by competent technical personnel. Sketches in 

the margin of the companion map illustrate 

possible results from these actions. In the paragraphs below, the selected landslide localities 

referred to in parentheses are described later in 

this report and are located on the companion 

map. 

Loading.-The most common loading (actually overloading) of a slope is by emplacing earth 

materials or slag as a fill, usually to extend the 

backyard of a house on the slope or on a ridgetop. Loading can cause the formation of surfaces of rupture in underlying soil and rock, 
resulting in failure. Structures also are loading 

factors. In most places they are set on bedrock, 

but when they are not, destruction may result 

-as occurred on Lawnwood Avenue (fig. 8; selected landslide locality 8). 

Cutting into a slope.-Because valleys of the 

region are rather narrow, excavation of the foot 

of a slope to make more flat ground is very common. This can be disastrous, particularly if the 

cut is in the toe of an unidentified prehistoric 

landslide deposit, as happened during construction of Interstate 79 (selected landslide locality 

2) and on West Smithfield Road (fig. 9; selected 

landslide locality 11). 

Placing fills on slopes.-Proper construction 

of a fill on a slope involves engineering practice, 

and should be designed for the particular slope 

on which it is to be placed; it includes removal 

of natural vegetation before emplacement and 

lift-by-lift compaction. If vegetation is not removed, surfaces of rupture or slip planes can 

form on decaying vege.tation between the new 

fill and the former natural slope; if fill is not 

compacted, failure can take place within it. The 

Painters Run (fig. 10) and Lawnwood Avenue 

(fig. 8) localities (selected landslide localities 5 

and 8, respectively) are examples of fill failure, 

as are many other residential and backyard fills 

in Allegheny County. 

Altering water conditions.-Natural slopes 

largely are protected from excessive infiltration 

of water by their vegetation; removal of vegetation can increase infiltration :and thus increase 

susceptibility to landsliding. Faulty drainage 

systems, such as inadequate disposal of downspout water, also can affect slopes. Alteration of 

FIGURE 8.-Landslide largely in fill, Lawnwood Avenue, Brentwood and Baldwin Boroughs. Warped wall of partially dismantled house in right foreground results from movement of footings that were not set in bedrock. 

House in right background is set on bedrock and apparently is not distressed structurally even though side and 

backyards have slipped away. Note large trees inclined strongly downslope behind car and house, evidence of a 

history of movement in the area. Photographed in April 1975. 

4 
FIGURE 9.-Active earthflow on south side of West Smithfield Road, between locality 11 and Boston. Toe is visible 

at base of slope from just above second car from right to just above the small car. Head is more than 100 feet 

upslope. Excavation that triggered earthflow was to valley-floor level as far back as small shed on slope. Left 

limit of earthflow is just to the right of shed, which itself has not moved appreciably. Note tilted trees on earthflow surface, and hummocky ground typical of surfaces of prehistoric landslides on :slope to left of shed. Photographed in April 1975. 

water conditions may have been a factor in the 

Baldwin Road, Robinson Township slide (selected landslide locality 3). 

WHAT THE BUYER, BUILDER, OR HOMEOWNER 

SHOULD LOOK FOR 

The buyer, builder, or homeowner must always bear in mind that areas susceptible to 

landslides commonly are larger than most individual properties. Thus, it pays to look not only 

at the property in question but also at adjacent 

areas, particularly those upslope and downslope. If the property slopes more steeply than 

about 15 p~rcent (15 feet of drop or rise vertically in 100 feet of horizontal distance), or if 

5 

adjacent uphill or downhill slopes (or both) are 

significantly steeper than the slope of the property, site examinations should be made. In addition, if the property is on relatively fiat ground 

on a ridge top or in a valley, but close to a fairly 

steep slope, an examination of the slope is 

recommended. It is most important to look for 

the features listed in areas labelled as highly 

sensitive on the companion map. 

The following features are indications that a 

property may have a potential or real landslide 

problem. All the features listed have been associated with landsliding in Allegheny County. 

If any of these are observed, the buyer, builder, 
FIGURE 10.-Landslide on Painters Run, Upper St. Clair Township. Debris at foot of slope partially blocks the creek, 

which is between camera station and slope. Note seepage from slope in left center; nearly horizontal bedrock exposed at right. House is set on bedrock and apparently is not threatened structurally. Photographed in April 1975. 

or owner should seek advice from competent 

technical personnel. 

(1) Cracks in buildings.-Most older buildings have minor cracks, but these probably result largely from normal settlement. In general, 

the fact that a building is old and shows no significant damage is an indication that the building probably will remain undamaged by landsliding. Many or large cracks in newer structures are reasons for concern, although the 

cause of cracking may well be something other 

than landsliding. Major cracks commonly are 

repaired by owners, but evidence of repair 

usually is visible on close examination. Wet 

basements may be evidence of cracks in 

foundation. 

(2) Cracks in brick walls around yards and 

6 

other outside br"ick and conc1·ete features.-

Vnlike buildings, which generally are set in 

bedrock, mos.t yard walls and other ancillary 

features rest on soil. They thus are sensitive to 

creep which can cause cracking or can pull such 

features away from structures. 

(3) Doors and windows that jam.-A door 

that sticks or otherwise does not seem to fit 

well or a sash window that jams may be evidence that the frame of a house has been 

warped. 

( 4) Retaining walls, fences, curbs, gas mete?·s, posts supporting porches, and other featwres out of plumb m· not ali ned in a normal 

way.-Fences and similar features usually are 

vertical and straight when built, curbs normally 

are straight, and gas-meter piping generally is 
horizontal when installed. Leaning fence posts, 

bowed fence or curb lines, and other departures 

from the expected thus require explanation. 

(5) Breakage of underground pipes and 

other· utilities.-Downslope movement can upset the alinement of buried utilities. For example, a pipeline parallel to a slope can be bowed 

by compression or strained by tension and ultimate breakage can result. Evidence of breakage 

includes otherwise unexplained wet ground, 

lowered water or gas pressure, and failure of 

service. 

(6) Leaky swimming and decorative pools.-

Concrete pools are rigid and tight when constructed. Soil movement can cause cracking, 

which creates an additional hazard in that water 

leaking from cracked pools can enter the ground 

and perhaps accelerate movement. 

(7) Tilted tr·ees, grapevines, reeds.-Trees 

are probably somewhat less reliable indicators 

of slope movement than are manmade objects, 

for trees on slopes tend to bend outward somewhat as they seek sunlight. However, trees leaning at appreciable angles (fig. 8) or numbers of 

trees leaning in different directions (fig. 9) 

strongly suggest areas of landsliding or strong 

creep. Many grapevines (fig. 11) and reeds have 

been observed on many prehistoric landslide deposits, perhaps as a result of water conditions 

within the deposits. They thus are general indicators of possible instability. 

(8) Tilted utility poles and taut or sagging . 

wires.-Most utility poles are more or less vertical and alined when new, and wires between 

poles usually sag uniformly, so appreciable tilting of poles and variations in amount of sag of 

FIGURE H.-Landslide on southeast-facing slope in Glenfield area extends almost from ridgetop to road. Note tilted 

and fallen trees on the landslide and grapevines on and adjacent to the landslide. Shed on left is on hummocky 

ground typical of surfaces of prehistoric landslide deposits. Relocation of the road in the foreground may have 

triggered the earthflow. Photographed from Interstate 79 in April 1975. 

7 
wires between adjacent poles are abnormal and 

noteworthy. 

(9) Cracks in the ground.-Cracks more or 

less parailel (across) to a slope usually are indications that the slope is moving. Unusually wide 

cracks are shown in figure 12. 

(10) Steplike ground featu?·es.-Slumping 

of ground usually results in steplike scarps (fig. 

2) that may range from very low to many feet 

high. When relatively new, the "risers" of the 

scarps usually expose fresh earth (fig. 13). 

Older scarps may have subdued angles because 

of erosion and may be vegetated, making them 

more difficult to identify. Whether old or new, 

these features are evidence of unstable 

conditions. 

(11) Hummocky ground.-Hummocks, low 

mounds, are common irregularly spaced features of the toes and lower ground surfaces of 

both prehistoric and recent landslides (fig. 9; 

fig. 13). They do not occur naturally on any 

other surfaces in Allegheny County. 

(12) Water seeps.-Seeps and springs are 

very common at the toes of landslide deposits. 

Water from seeps on upper slopes may saturate 

the ground and so contribute to the mobility of 

downslope materials (fig. 10). Swampy ground 

and small and perhaps short-lived areas of 

ponded water are common evidences of groundwater seepage on slopes. 

GEOLOGIC FACTORS AFFECTING 

SUSCEPTIBILITY TO LANDSLIDING 

IN ALLEGHENY COUNTY 

Bedrock in Allegheny County is entirely composed of coal-bearing rocks of Pennsylvanian 

and Permian age (between 320 and 225 million 

years ago). Formation names, from oldest to 

youngest, are the Freeport in the Allegheny 

Group, the Glenshaw and the Casselman in the 

FIGURE 12.-View southwestward down cleared pipeline path toward Fallen Timber Ru n and Pennsylvania 

Highway 51, visible through trees. Ground cracks as much as 10 feet wide parallel ac ro~s slope . Note segments 

o~ bro~en and abandoned pipe in foreground crack and in background crack near foot of man. Replacement 

pipe laid on surface. Photographed in April 197 5. 

8 
Conemaugh Group, the Pittsburgh and the 

Uniontown in the Monongahela Group, and the 

Waynesburg and the Washington in the Dunkard Group. Their relations and general distribution are shown in the columnar section and 

small-scale geologic map that accompany the 

companion map. The reader is referred to 

"Geology of the Pittsburgh area" (Wagner and 

others, 1970) for a thorough description of the 

general geology. 

Significant factors bearing on landslide susceptibility include: 

(1) Rock types.-Rocks appearing at the 

surface are mostly sandstone, siltstone, shale, 

claystone, and limestone. Coal constitutes less 

than 2 percent of the rocks exposed in the area. 

Of particular significance to slope stability are 

widespread red beds, dusky red layers of claystone and shale, thickest and most consistent 

near the top of the Glenshaw Formation, but 

also common in the lower part of the Glenshaw 

and in the basal and upper middle parts of the 

Casselman Formation. Red beds also are present 

sporadically in the lower Pittsburgh Formation 

and other parts of the stratigraphic section. No 

sensitive red beds are known in the Freeport 

Formation. As shown on the companion map, 

landslides clearly are most common on deeply 

weathered red-bed slopes, but thick beds of gray 

to brown claystones in the Monongahela Group 

and the lower Washington Formation of the 

Dunkard Group also weather rapidly and underlie extensive areas where slopes are unstable. 

Sandstone and limestone commonly are harde1· 

and more resistant to weathering than are siltstone, claystone, and shale. This explains why 

sandstone and limestone form ledges and cliffs 

on many slopes, whereas other rock types rarely are well exposed except in cut banks of 

streams, in other very steep natural slopes, and 

in manmade exposures such as highway cuts. 

The distribution of rock types and their general 

engineering characteristics have been summarized by Kohl and Briggs (1975) on a map of 

Allegheny County at the same scale as the companion map. 

FIGURE; 13.-Slumped area above northwest-facing roadcut; for northbound lane of Interstate 79, Glenfield area. Scarps 

define ~lump blocks on which tilted trees are in contrast to upright trees on undisturbed slopes above. Note 

small scarps and hummocky ground below trees and above bench. Photographed in April 1975. 

9 
(2) Rock layering.-Rock types alternate 

and form layers that are eommonly 1 inch to 10 

feet thick (fig. 10), but in places, layers are 

thicker than 30 feet. Some rock layers are traceable for miles, but most sandstone layers, for 

example, grade laterally into anotherr rock type 

in short distances, and some conspicuous lateral 

changes in rock types can be seen in a single 

exposure. If, for example, a red-bed layer beneath a sandstone layer is decomposed by 

weathering, then the overlying hard rock is less 

firmly supported and may move downslope in 

response to gravity. 

(3) Rock fractures.-Two types of rock 

fracture occur: faults-fracture's along which 

rocks on one side are offs,et from rocks on the 

other side; and joints-tight to open fractures, 

--along which no evidence of movement can be 

seen. Open joints are those in which rocks on 

either side are sufficiently far apart to allow 

relatively free passage of air or water. Along 

tight joints, rocks on either side are in close 

contact with each other. Faults are relatively 

rare in Allegheny County. The harder rock layers, composed of sandstone and limestone, are 

well jointed in outcrop, joints commonly being 

open and spaced one to several feet apart. Closely spaced joints occur in many siltstone, claystone, and shale layers, but most of these joints 

are tight. Most joints are nearly perpendicular 

to the plane of layering. Joints contribute to 

landslide susceptibility, for if rock layers were 

not jointed, their tendency to break off when 

underlying rock is removed would be less. Open 

joints are also an important factor in rock 

permeability. 

(4) Attitude of rock layering.-Most rock 

layers in Allegheny County are tilted at such 

small angles from the horizontal that their attitude can best be measured in feet per mile 

rather than in degrees or in percent of grade 

(fig. 10). Rock attitude is mos,t critical to landsliding on slopes where rock layers dip in the 

same general direction as the slopes but at 

lesse~r angles than the slopes, for on such overdip slopes, ground-water discharge is enhanced, 

and water is an important factor in most landslides (Briggs, 197 4). 

(5) Soil cover.-Soils are composed chiefly 

of fine-grained mineral constituents derived 

from rock decomposition during weathering. 

However, the term "soil" means different things 

to different people. To a soil_ scienti~st, soil means 

the material that supports plant life and that 

has undergone near-surface zonation resulting 

from the interaction of clfmate and living matter, conditioned by slope and relief. An agricultural soil rarely is more than 6 feet deep and 

may rest on and be developed from a parent 

material that is itself decomposed rock. To an 

engineer, soil includes all unconsolidated material above hard bedrock, and so includes the 

parent material of many agricultural soils. Only 

where depth to hard bedrock is relative,ly shallow will there be virtual agreement between a 

soil scientis,t and an engineer as to thickness 

and composition of a soil. "Soil" is used in this 

report in the engineering sense; it thus applies 

not only to material resulting from rock weathering in place, but also to masses of fragmented 

and decomposed rock particles that have been 

transported and redeposited elsewheTe. Examples of transported soils are colluvium (soil accumulated at the base of slopes) and alluvial 

terrace deposits (deposited from running wate~r) . Borth of these types can be subject to 

land sliding. 

In Allegheny County, soils of the hilltops are 

relatively thin, less than 6 feet thick in many 

areas. Soils of hill slopes are absent where bedrock crops out, are relative,ly thin on many upper slopes, and are made up of more than 20 

feet of colluvium on many lower slopes. Valleybottom soils generally have nearly level surfaces 

and so are not a significant factor in most landsliding; they may exceed 100 feet in thickness. 

The composition of a soil reflects the composition of the rock from which the soil was derived, for sandstone will we~ather to a sandy 

soil, shale to a clayey soil, and hard blocky rocks 

may weather to a rocky soil. Most soils are 

loose to moderately cohesive and are finer 

grained near the surface than they are at depth. 

They will not stand long on s1teep slopes, and, 

in Allegheny County, soils weathered from red 

beds and, to a somewhat lesser extent, limestone 

are particularly sensitive to undercutting, overloading, or other processes. Clayey soils when 

dry commonly are crumbly and relative•ly low in 

weight per unit volume. When wetted, clay 

10 
soils retain water and so become heavier, become plastic, and, depending on their mineral 

composition, may become very slippery. Many 

wet clayey soils resemble modeling clay in feel, 

relative weight, and plasticity. 

(6) Permeability of rocks and soils.-P.ermeability as used here means the capacity of 

bedrock and soil to transmit water. Sandstone 

in the county commonly is moderately permeable; water may pass around grains of sand and 

through voids between the grains. In addition, 

sandstone layers may have open joints that 

facilitate passage of water. Limestone is fine 

grained, and solid unfrac_tured limestone is more 

or less impermeable. However, most layers of 

limestone are permeable because they are closely jointed, and these joints commonly are open 

because of dissolution and removal of minerals 

by moving ground water. In contrast, siltstone 

and shale are fine grained and tightly jointed; 

they commonly are less permeable than most 

coarser grained rocks. Similarly, most sandy 

and rocky soils are more permeable than are 

soils composed largely or entirely of clay. Rocks 

and soils are most likely to be saturated by 

water in zones where permeable materials overlie relatively impermeable materials. Complete 

saturation commonly re~sults in increased pore 

pressure's that decrease cohesiveness between 

particles and increase buoyancy in the saturated 

material. The effect is similar to lubrication and 

enhances susceptibility to landsliding. 

Permeability of rocks and soils and other 

facets of the shallow ground-water regime relevant to the landsliding process have been described in greater detail by Subitzky (1974a, b, 

c). 

(7) Steepness of slopes.-Allegheny County 

is a land of hills and ridges separated by valleys 

through which streams and rivers flow at levels 

commonly 300 feet, and locally more than 600 

feet, below adjacent ridge crests. The valley 

walls are relatively steep; slopes of 25 percent 

(25 feet of drop in 100 feet of horizontal distance; about 14°) or greater occupy about onefourth of the area. These steep natural slopes 

are leading factors in the occurrence of landslides, for if the area were largely one of relatively flat or gently sloping land surfaces, it is 

unlikely that even red beds would become involved in significant landsliding on natural 

slopes. 

Relative importance of factors.-All the 

above stated factors are interrelated. At a given 

place, one factor may be the chief control of 

susceptibility to landsliding, whereas at another 

place, the same factor may be less important 

than others. For example, where a major stream 

is undercutting its bank by flowing against it, 

oversteepening will occur and slope failure ultimately will ensue regardless of whether the 

bank material is rock or soil; where a thick soil 

cover becomes saturated with water, failure 

may occur even on relatively gentle slopes. Some 

slopes can be consistent landslide hazards because of natural or manmade steepness or excessive rock fracturing; some overdip slopes, on 

the other hand, may be less susceptible to landsliding because only one type of rock is present. 

SELECTED LANDSLIDE LOCALITIES 

Given below are brief descriptions of 15 localities that are examples of landsliding types and 

effects in Allegheny County. The companion 

map shows the localities by number; general 

locations are shown on figure 14. In addition, 

word descriptions are sufficient for location with 

the assistance of road maps of Pittsburgh and 

vicinity issued by oil comp~anie~s. Included are 

some localities described in greater detail by 

others (chiefly Ackenheil, 1954), as well as 

localities identified during the current study. 

(1) Sewickley Water Works area Nevin 

Avenue-Waterworks Road, Borough of Sewickley.-The base of a recent landslide on the south 

wall of the valley near the westernmost impoundment is at an altitude of 850 feet; it~s head 

is at approximately 950 feet with a scarp in red 

beds at the edge of an upper road. Waterworks 

personnel report that the slide took place in 

summer 1973 after heavy rains. A major factor 

in sliding appears to be infiltration of water 

from above into the landslide mass. Layers of 

red mudstone exposed above the scarp locally 

dip 15° SW. and appear to be part of an older 

landslide deposit. The valley has many prehistoric landslide areas, and both sides of the valley 

have hummocky lower slopes and typically thick 

colluvial deposits. An older (1940) landslide on 

the north side of the valley just upstream from 

11 
the same impoundment is a classic example of 

the effects of unusually heavy rainfall combined 

with man's modification of a sensitive slope. 

Loading of the red-bed slope with sandstone 

quarry waste was compounded by additional 

loading and an unusual degree of saturation 

owing to an unusually high amount of precipitation for the day of the event as well as for the 

previous week and month. As documented by 

Ackenheil (1954), the combined loading caused 

a landslide of an estimated 350,000 cubic yards 

40" 

30' 

0 5 10 MILES 

0 5 10 KILOMETRES 

that ruined one reservoir. The sandstone rubble 

overlying the affeeted slope is considerable. In 

winter, dense misty patches caused by warm-air 

exhalations into colder air demonstrate the 

existence of extensive interconnecting voids in 

the landslide mass. 

(2) Interstate 79 (279), Glenfield a1·ea about 

1 mile north of the Ohio River.-During earthwork for highway construction, prehistoric 

landslide masses in red beds were excavated. 

Oversteepening of slopes of these highly sensi-

~~!: "': ~ J;>AI'I~ . 

15. 

FIGURE 14.-Map of Allegheny County, showing locations of selected landslide localities. 

12 
tive materials resulted in serious and recurring 

landslide problems (fig. 11; fig. 13; Hamel and 

Flint, 1969). 

(3) Baldwin Road, Robinson Township, 

about 1,4 mile north of Penn-Lincoln Parkway, 

"Parkway West." -Along the southeast side of 

the apartment complex on the northwest side of 

Baldwin Road is a steep fill slope in which some 

slumping occurred. Brick walls of some units of 

the complex cracked, and slumping forced removal of back porches of several units. Additions to downspouts we,re made to direct water, 

a possible causative factor in the slumping, 

away from foundations. A concrete retaining 

wall between the lowest developed level and the 

second level was distressed (fig. 15). The Pittsburgh coal bed here is at or slightly below the 

level of the lowest buildings of the complex, and 

the coal has been mined out, according to information from the Pennsylvania Division of 

Mine Subsidence Regulation. Possible mine subsidence, soil creep, and landsliding, and the potential for lateral spreading under footings may 

have combined to make assurance of structural 

integrity more difficult here than elsewhere. 

( 4) Narrow ridge between Chartiers Creek 

and the N01·folk and Western Railway, Scott 

Township, just east of Borough of Heidelberg. 

-Surface cracks in this ridge are similar to but 

smaller than cracks on the slope at locality 10 

and may also indicate slope failure (John Reynolds, oral commun., 197 4). However, the top of 

the ridge is only about 30 feet above the Pittsburgh coal bed, mined out in this area, so subFIGURE .15.-Distressed concrete retaining wall near Baldwin Road, Robinson Township, which has m1ssmg key 

block at bottom of third segment from right. Vertical buttresses aid in repair effort. Note saplings leaning 

strongly downhill at left. Photographed in April 1975. 

13 
sidence of the surface because of undermining 

may be responsible for these phenomena. 

(5) Painters Run Road, Upper St. Clair 

Township, about 14, mile east of Bower Hill 

Road.-The landslide on the northeast side of 

the creek (fig. 10) formed in 1971 after a fill 

was placed to extend the backyard of the house 

at the top of the bluff. The fill failed shortly 

afterwards, and additional fill was placed. During tropical storm Agnes in 1972, the landslide 

mass moved down to the creek, leaving a bedrock face exposed. Since then, the fill on the 

flat above has slumped, forcing a change in the 

alinement of a fence. The rocks on which the 

slide formed are in the middle part of the Monongahela Group, about 100 feet above the 

Pittsburgh coal bed, which is exposed at ro,ad 

level on the south side of the road. 

(6) Kilbuck Drive just opposite the Maintenance Office fo1· Riverview Park, City of Pittsburgh.-The toe of a large landslide, very active 

in early 1974, encroached on the road (fig. 16). 

The head of the landslide is near an apartment 

complex on the ridge above, and it can be viewed 

from the north end of the parking area of the 

complex. The lower half of the slope is underlain by red beds, and the upper slope is underlain by interlayered gray claystone and red 

beds. Evidence of distress to structures in the 

complex included wall cracks, and one pier out 

of plumb. Immediately south of the apartment 

complex is the scar of a very large 1949 landslide documented by Ackenheil (1954). 

(7) Bigelow Boulevard, City of Pittsburgh, 

in line with 24th Street, southeast of Allegheny 

River.-This massive fill failure had its beginnings when the boulevard was constructed in 

1896. Fill deposited then and later had a history 

of movement that culminated in late 1920, when 

the toe encroached on the Pennsylvania Railroad (now Penn Central Transportation Company) yard at rates as fast as 12 inches per 

hour. More than 200,000 cubic yards of material 

was involved. When asked what could be done 

FIGURE 16.-Toe of landslide encroaches on Kilbuck Drive opposite park maintenance office adjacent to fence at left 

edge of picture. Car on right is parked at right edge of road, which was two lanes wide and straight before 

landsliding. Continuous excavation is required to keep road open. Photographed in April 1975. 

14 
to remedy the landslide, General G. W. Goethals 

of Panama Canal fame is said to have answered, 

"let 'er slide" (Ackenheil, 1954). 

(8) Lawnwood Avenue, Boroughs of Brentwood and Baldwin.-Failure after placing foundation footings on fill is well illustrated here 

where three houses have been destroyed and a 

fourth appears to be in danger (fig. 17). The 

first fill was placed across a narrow valley on the 

slope. The houses were built in the 1960's; footings were placed in the old fill, and backyards 

were built up by emplacement of additional fill. 

Movement began shortly after the houses were 

completed, when the backyards slumped. The 

backyards were built up again, but further 

movement occurred, and by June 1972, two 

houses were so damaged that they were abandoned. The third house, on the east, was evacuated in February 1974, when the back wall 

began to collapse (fig. 8). The fourth house, on 

the west, had suffered no apparent structural 

damage and was still occupied in late 1974. However, the side yard and part of the backyard had 

slumped away, exposing part of the foundation 

(fig. 8). Downslope movement in this area is not 

all recent, as is well indicated by large trees 

leaning strongly downhill a short distance to 

the west (fig. 8). The Pittsburgh coal bed has 

been mined out beneath this area, and mine 

drainage is evident at the foot of the slide. 

Lubrication and increased buoyancy from mine 

waters may be factors in the Lawn wood A venue 

landslide (Craft, 1974). 

(9) Brilliant Cut, City of Pittsburgh, about 

lf:"! mile east of Highland Park Bridge.-The 

massive failure of about 110,000 cubic yards of 

rock blocked the Pennsylvania Railroad (now 

Penn Central Transportation Company) tracks 

in 1941. Failure has been attributed to introduction of water through open joints, resulting in 

movement along a failure plane which had 

formed in red beds and gray shale (Ackenheil, 

1954; Hamel, 1972). Although evidence of the 

landslide long since has been obscured, this 

FIGURE 17.-Landslide on Lawnwood Avenue, Brentwood and Baldwin Boroughs, from base of slope. Fallen trees in 

foreground are in toe of landslide. House in center is in right background of figure 8. Clearly shown is undercutting of slabs in backyard of this house. Area to right of house was occupied by three houses destroyed by landsliding. Photographed in April 1975. 

15 
locality remains one of the better exposures of 

this part of the rock sequence. 

(10) Fallen Timber Run, Elizabeth Township, about 1!2 mile southeast of the Monongahela River.-Houses at the top of the slope on 

the northeast side of the valley may be in danger from a complex slope failure. In mid-197 4, 

there was no conspicuous structural damage to 

any house, but at least one house appeared to 

be moving; the owner had to relevel appliances 

several times. Backyards made on fill have 

slumped, forming escarpments and cracks in 

soil. Cracks as much as 10 feet wide, 30 feet 

deep, and many tens of feet long, as shown in 

figure 12, have opened in soil and rock on the 

slope between the houses and the valley. Earth 

material was encroaching on buildings in the 

valley, and at the time of writing (197 4), several governmental agencies were investigating 

this area; studies included periodic use of precision surveying instruments to measure displacements. Because the nature and extent of 

this landslide are not yet clearly known, the 

area is indicated on the companion map as a 

prehistoric landslide on which recent landslides 

have been superimposed. The area is underlain 

by rocks of the Casselman Formation. 

(11) West Smithfield Road, Borough of Lincoln, 1,4 to 1 mile southwest of Boston.-Hummocky ground, characteristic of prehistoric 

landslides on red beds, is wen developed on the 

northwest side of valley. Grapevines and tilted 

trees are common. A recent earthflow is well 

exposed on the south side of the road, near 

Boston (fig. 9). 

(12) Russian Hill, Borough of Wilmm·ding, 

just n01·thwest of intersection of Pennsylvania 

Highway 130 and Wilmerding Road.-Houses 

built many decades ago on a steep slope underlain by red beds were unaffected by their location until late winter 1971, when excavation upslope altered natural drainage (Kelley, 1971). 

Movement of red-bed soil damaged and forced 

abandonment of some houses. In 197 4, damage 

on Laveen Street still was conspicuous. 

(13) Intersection of U.S. Highway 30 and 

Pennsylvania Highway 48, North Versailles 

Township.-In 1968, shortly after the shopping 

center on the northeast corner was built, about 

75,000 cubic yards of fill slumped into the '~alley, 

carrying away the eastern part of the parking 

lot. Attempts to rebuild the parking area have 

resulted in renewed movement. The base of the 

fill was on rocks of the Casselman Formation. 

Features of the landslide area include intermittently ponded water near its eastern edge. 

(14) Glass1nere vicinity, East Dee1· Township.-The very steep east .. facing slope from 

the vicinity of the west end of the New Kensington bridge northward to Crawford Run has a 

long history of slope-stability problems, as is 

indicated by widespread prehistoric landslide 

deposits, at least one abandoned property near 

the bridge, and buckled and displaced retaining 

walls. The extremely heavy rains accompanying 

tropical storm Agnes, in June 1972, triggered 

further landslides that resulted in destruction 

of one house. damage to others, and temporary 

blocking of Freeport Road. Bedrock of the lower slopes largely is composed of red beds. 

( 15) Elliot Road, just n01·th of the Wnlia,m 

Penn Highway, Borough of Monroeville, about 

1 mile east of Pennsylvania Tu1·npike ove1·pass. 

-Red beds weathered to an 8- to 15-foot-thick 

silty-clay soil are exposed in a shallow borrow 

pit. Beneath the soil, the red beds are weathered 

to a crumbly slippery mass. Deeply weathered 

gray and yellow-brown shales also are exposed. 

A small, recent landslide extends from the east 

end of the pit to the old William Penn Highway. 

This locality provides the interested observer 

with a good opportunity to examine types of 

material involved in many landslides in Allegheny County. 

GLOSSARY 

Alluvium.-A general term for unconsolidated 

fine- to coarse-grained sediment deposited 

during comparatively recent geologic time 

by running water in the bed of a river or 

stream, on a flood plain adjacent to a river 

or stream, or in related environments of 

_c;leposi tion. 

Anticline.-A fold of rock layers that is convex 

upward, opposfte to the form of a syncline. 

Bedrock.-A general term for the rock, usually 

solid, that underlies soil or other unconsolidated surficial material. 

Clay.-A loose earthy aggregate of mineral or 

rock particles most of which are less than 

16 
1/256 mm in diameter. Commonly composed chiefly of clay minerals and quartz. 

Claystone.-A rock composed of indurated clay. 

Contact.-A boundary between different rock 

units. 

Dip.-The angle by which the plane of rock layering (or other planar element, such as a 

joint) is inclined from the horizontal. Commonly expressed in degrees or in feet per 

mile. 

Fault.-An earth fracture along which materials on one side have been displaced relative 

to those on the opposing side. Displacement 

can range in scale from inches to many 

miles. 

Formation.-The basic rock-stratigraphic unit 

in the local classification of rocks. Commonly of considerable thickness and lateral 

extent and commonly shows distinct differences in rock type or proportions of rock 

types from formations immediately above 

and below. 

Geomorphology.-The definition and description of the configuration of the Earth's 

surface. 

Group.-A major rock-stratigraphic unit consisting wholly of two or more contiguous or 

associated formations having significant 

rock features in common. 

Indurated.-Descriptive of rock material hardened by the action of heat, pressure, or the 

introduction of some cementing compound 

not commonly contained in the original 

material. 

Joint.-A fracture or parting in a rock in which 

rock on one side has not been displaced 

relative to rock on the opposing side. Usually planar or gently curved. Joints often 

occur in parallel sets in which spacing between joints is more or less regular. Spacing between joints varies widely in different rock types. 

Limestone.-A rock consisting of more than 50 

percent calcium carbonate, primarily in the 

form of the mineral calcite. 

Member.-A subordinate rock-stratigraphic 

unit constituting some specially developed 

part of a formation. Commonly of moderate 

lateral extent and apprectably thinner than 

the formation of which the member is a 

part. 

Mineral.-A naturally formed inorganic compound that has either a definite chemical 

composition or a composition that ranges 

between definite limits and that bar, usually, a characteristic crystal form. 

Permeability.-In rocks and soil, the cap~city to 

transmit water. The greater this capacity, 

the greater the perm-eability. 

Rock.-Any naturally formed, consolidated or 

unconsolidated (loose) material generally 

composed of two or more minerals, occasionally of one mineral. 

Sand.-A loose aggregate of mineral or rock 

particles, most of which range from 1/16 

mm to 2 mm in diameter. The mo"'t common mineral in sand is quartz. 

Sandstone.-A rock composed of in~urated 

sand. 

Shale.-In usage common to the area, shale is 

moderately well indurated rock which is 

composed mostly of clay and silt-sh~ed particles, which commonly is thinly or very 

thinly layered, and which commonly breaks 

down upon weathering to platy fr2 ~ents 

oriented parallel or subparallel t.o rock 

layering. 

Silt.-A loose aggregate of mineral or rock particles, most of which range from 1/256 to 

1/16 mm in diameter. 

Siltstone.-A rock composed of indurated silt. 

Stratigraphic.-Adjective descriptive of geologic features and concepts reh'.ted to 

stratigraphy. 

Stratigraphy.-The definition and description of 

major and minor natural divisions in layered rocks, such as groups, formatk'ls, and 

members. 

Surficial deposits.-Unconsolidated or weakly 

consolidated earth materials that rest on 

bedrock. 

Syncline.-A fold of rock layers that is concave 

upward. For example. in cross section, a 

tightly folded syncline would have tl'e form 

of the letter U. 

Terrace deposit.-Alluvial deposits on re1atively 

level, commonly bench-shaped surfr.~es adjacent to river and stream valleys, gimerally at altitudes well above those reached 

by historic floods. Terrace alluvium. 

17 
REFERENCES CITED 

Ackenheil, A. C., 1954, A soil mechanics and engineering geology analysis of landslides in the area of 

Pittsburgh, Pennsylvania: Pittsburgh, Pa., Univ. 

Pittsburgh, Ph.D. dissert., 121 p. (Ann Arbor, 

Michigan, Univ. Microfilms, Pub. no. 9957, 1962.) 

Ackenheil, A. C., and Associates, Inc., 1968, Mining and 

physiographic study, Allegheny County, Peimsylvania for the Board of County Commissioners: 

Pittsburgh, Pa., 45 p., maps. 

Briggs, R. P., 1974, Map of overdip ;slopes that can 

affect landsliding in Allegheny County, Pennsylvania: U.S. Geol. Survey Misc. Field Studies Map 

MF-543. 

Craft, J. L., 1974, Is a geologic evaluation of a development site needed?: Pennsylvania Geology, v. 5, ·no. 

3, p. 2-5. 

Eckel, E. B., ed., 1958, Landslides and engineering practice: Natl. Research Council, Highway Research 

Board Spec. Rept. 29 (Natl. Acad. Sci.-Natl. Research Council Pub. 544) , 232 p. 

Fisher, S. P., Fanaff, A. S., and Picking, L. W., 1968, 

Landslides of southeastern Ohio: Ohio Jour. Sci., 

v. 68, no. 2, p. 65-80. 

Hamel, J. V., 1970, Stability of slopes in soft altered 

rocks: Pittsburgh, Pa., Univ. Pittsburgh, Ph.D. dissert., 305 p. 

--- 1972, The .slide at Brilliant cut, in Stability of 

rock slopes-Proceedings of the 13th Symposium on 

Rock Mechanics, Urbana, Illinois, 1971: New York, 

Am. Inst., Mining Metall., Petroleum Engineers, 

Soc. Mining Engineers, p. 487-510. 

Hamel, J. V., and Flint, N. K., 1969, Analysis and de-

·sign of highway cuts in rock: a slope stability study 

on Interstate Routes 279 and 79 near Pittsburgh, 

Pennsylvania: Pennsylvania Dept. Highways Research Proj. no. 41472, 130 p. 

--- 1972, Failure of colluvial slope: Am. Soc. Civil 

Engineers, Soil Mechanics and Foundations Div. 

Jour., v. 98, no. SM2, p. 167-180. 

Kelley, D. R., 1971, Wilmerding landslide, cooperative 

Pennsylvania Geological Survey emergency effort: 

Pennsylvania Geology, v. 2, no. 3, p. 11-12. 

Kohl, W. R., and Briggs, R. P., 1975, Map of rock types 

in bedrock of Allegheny County, Pennsylvania: U.S. 

Geol. Survey Misc. Field Studies Map MF-685A. 

Myers, C. K., 1935, The red beds of the Pittsburgh quadrangle: Pittsburgh, Pa., Univ. Pittsburgh, Ph.D. 

dissert., 56 p. 

Nilsen, T. H., 1972, Preliminary photointerpretation map 

of landslide and other surficial deposits of parts of 

the Los Gatos, Morgan Hill, Gilroy Hot Springs, 

Pacheco Pass, Quien Sabe, and Holl :<!ter 15-minute 

quadrangles, Santa Clara County, California: U.S. 

Geol. Survey Mi:sc. Field Studies Map MF-416, 2 

sheets, scale 1 : 62,500. 

Philbrick, S. S., 1959, Engineering geology of the Pittsburgh area, in Geol. Soc. America, Guidebook for 

field trips, Pittsburgh Meeting, 19~f9-Field Trip 

no. 6: p. 189-203. 

--- 1960, Cyclic sediments and engin~ering geology: 

Internat. Geol. Cong., 21st, Copenhag~n, 1960, Rept., 

pt. 20, p. 49-63. 

Pomeroy, .J. S., 1974, Landslide suscep4:ibility map of 

the Pittsburgh West 7%-minute quadrangle, Allegheny County, Pennsylvania: U.S.- Geol. Survey 

open-file report 74-228, 16 p., 1 pl., 7 figs. 

Pomeroy, J. S., and Davies, W. E., 1975, Map of susceptibility to landsliding, Allegheny County, Pennsylvania: U.S. Geol. Survey Misc. Field Studies 

Map MF-685B [in press]. 

Sharpe, C. F. S., 1938, Landslides and related phenomena; a study of mass-movements o:" soil and rock: 

New York, Columbia Univ. Press, 136 p. [reprinted 

1960, Paterson, N.J., Pageant Books]. 

Subitzky, Seymour, 1975a, A summary of behavior of 

the hydrologic regime as related to land-use characteristics, Allegheny County, Penr~ylvania: U.S. 

Geol. Survey Misc. Field Studies Map MF-641A 

[in press]. 

--- 1975b, Hydt·ogeologic framework and generalizedshallow ground-water circulation sy~tem, Allegheny 

County, Pennsylvania: U.S. Geol. Survey Misc. 

Field Studies Map MF-641B [in press]. 

--- 1975c, Heavy storm precipitation and related 

mass movement, Allegheny County, Pennsylvania: 

U.S. Geol. Survey Misc. Field Studies Map MF641D [in press]. 

U.S. Soil Conservation Service, 1973a, Volume 1, Soil 

survey maps for Allegheny County, Pennsylvania: 

Washington, D.C., U.S. Govt. Prhting Office, p. 

1-7, 243 p. of maps. 

--- 1973b, Volume 2, Soil survey interpretations for 

Allegheny County, Pennsylvania: Washington, D.C., 

U.S. Govt. Printing Office, p. 1-120, G1-G7. 

Wagner, W. R., Heyman, Louis, Gray, R. E., Belz, D. 

J., Lund, Richard, Cate, A. S., and Edgerton, C. D., 

1970, Geology of the pittsburgh arei1-: Pennsylvania 

Geol. Survey, 4th ser., Gen. Geol. Rent. G 59, 145 p. 

Winters, D. M., 1972, Pittsburgh red bed~-Stratigraphy 

and slope stability in Allegheny County, Pennsylvania: Pittsburgh, Pa., Univ. Pi~tsburgh, Ph.D. 

dissert., 49 p. 

18