Geologic and 

Hydrologic 

Map Reports 

for Land-Use 

Planning in 

the BaltimoreWashington 

Urban Area 

GEOLOGICAL SURVEY 

CIRCULAR 806 

Geologic and Hydrologic Map Reports 

for Land-Use Planning in the 

Baltimore-Washington Urban Area 

By A. J. Froelich, J. T. Hack, and E. G. Otton 

GEOLOGICAL SURVEY CIRCULAR 806 

Examples of how geologic and hydrologic map reports on 

1\lontgomery and Prince Georges Counties, Nid., can be 

used to help identify and solve land- and water-use problems 

1980 
United States Department of the Interior 

CECIL D. ANDRUS, Secretary 

Geological Survey 

H. William Menard, Director 

Library of Congress Cataloging in Publication Data 

Froelich, Albert Joseph, 1929-

Geologic and hydrologic map reports for land-use planning in the Baltimore-Washington urban area. 

(Geological Survey circular ; 806) 

Bibliography: p. 

1. Geology-Maryland-Baltimore metropolitan area. 2. Geology-Washington Metropolitan area. 3. Hydrology-Maryland-Baltimore met11opolitan area. 4. HydrologyWashington metropolitan area. 5. Land use-Planning-Maryland-Baltimore metropolitan area. 6. Land use-Planning-Washington metropolitan area. I. Hack, John 

Tilton, 1913- joint author. II. Otton, Edmond George, 1918- joint author. 

III. Title. IV. Series: United States. Geological Survey. 

Circular ; 806. 

QE75.C5 no. 806 [QE122.B33] 557.3'08s 79-13766 [912' .1 '62415109752] 

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

1200 South Eads Street, Arlington, VA 22202 
CONTENTS 

Page 

Introduction 1 

Geologic setting of the Baltimore-Washington urban area -------------------- 5 

Hydrologic cycle in the Baltimore-Washington urban area ------------------- 6 

The use of map reports for the appraisal of some common land-use problems__ 8 

Slope-stability problems ___ ______ _ ____ __ ______ ____ ___ _____ __ _ _______ ___ 8 

Foundation conditions ________________ --------------------- ___ ___ ______ 11 

Tunneling conditions ______________________________________ ------------ 13 

Ground-water availability _ _ _ __ _ _ _ _ _ _ __ _ _ _ _ _ __ _ _ _ __ _ _ _ _ __ _ _ _ _ _ __ _ __ _ _ _ _ 13 

~ontgomery County----------------------------------------------- 13 

Prince Georges County -------------------------------------------- 14 

Construction materials and mineral resources --------------------------- 15 

Drainage basins, land-use planning, and zoning ------------------------- 18 

Problems of valley-bottom lands --------------------------------------- 19 

Sanitary-landfill sites ____ ________ ____ _____ _____ _____ ___ ______ __ _______ 20 

Computer mapping and land-use planning ------------------------------ 21 

References cited ______________ ---------- __ _____ ___ __ _ _ __ _ _ ___ __ __ _________ 24 

ILLUSTRATIONS 

Page 

CoVER. Collage of aerial views of Washington, D.C., and vicinity 

FIGURE 1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

Index map showing areas mapped during the Baltimore-Washington Urban Area Study ----------------------------------- 2 

Generalized geologic map of ~ontgomery and Prince Georges 

Counties, ~d --------------------------------------------- 7 

Diagrammatic· section in the Baltimore-Washington urban area 

showing major geologic features and the hydrologic cycle ____ 8 

Graph showing water budget for the Patuxent River basin above 

the Unity gaging station ---------------------------------- 9 

Block diagram of hypothetical area in ~ontgomery County showing examples of common surface materials that overlie bedrock ----------------------------------------------------- 10 

Photograph of a landslide in Cretaceous clay, southeast Washington, D.C., adjacent to Prince Georges County line ------------ 11 

Diagrammatic section across ~ontgomery and Prince Georges 

Counties showing occurrence of construction materials and rock 

and mineral resources ------------------------------------- 16 

Aerial view of quarry in serpentinite west of RockviHe, ~ontgomery County------------------------------------------- 17 

Aerial view of gravel pits, northern Prince Georges County _____ 18 

Photograph showing coarse sand and gravel overlain by fine sand 

and silt exposed in a pit in southeastern Prince Georges 

County -------------------------------------------------- 19 

Photograph of a completed sanitary landfill at Oxon Run, Prince 

Georges County ______ _____ _____ _____ _ _________ _ __ _ __ _ ___ __ 21 

Computer composite map showing some of the conditions affecting 

sanitary-landfill sites, ~ontgomery County ------------------ 22 

iii 
TABLES 

TABLE 1. Reports containing information on the geology, the hydrology, the 

mineral resources, and land-use planning in the BaltimorePage 

Washington urban area ----------------------------------- 3 

2. Representative institutional users of geologic and hydrologic map 

reports -------------------------------------------------- 5 

iv 
Geologic and Hydrologic Map Reports for Land-Use 

Planning in the Baltimor'e-Washington Urban Area 

By A, J. Froelich, J. T. Hack, and E. G. Otton 

INTRODUCTION 

Decisionmakers and land-use planners in the 

rapidly urbanizing counties near the Nation's 

Capital have been aware of physical limits and 

hazards to land and water development for 

many years ; however, geologic and hydrologic 

information in understandable form on which 

to base decisions has not been available to 

them until recently. In 1971, the U.S. Geological Survey (U.S.G.S.), in cooperation with 

the Maryland Geological Survey (M.G.S.), initiated the Baltimore-Washington Urban Area 

Study, a pilot project to determine the usefulness of geologic and hydrologic data in helping 

solve problems of land and water use. The 

objective of this project was to provide relevant and timely information particularly useful for county and regional planning and plan 

implementation. The project was not designed 

to supplant detailed site studies that are needed 

before and during specific development. 

Within the overall Baltimore-Washington 

Urban Area Study, the U.S.G.S. focused its 

efforts on studies in Montgomery and Prince 

Georges Counties, Md., and on a more detailed 

study of adjacent Washingon, D.C. (fig. 1). 

The M.G.~., which has initiated a long-range 

program of geologic studies for land-use planning, undertook detailed studies in Baltimore 

County, Md. (fig. 1). A less detailed geologic 

map of Baltimore County was also completed 

(Crowley and others, 1976). In all, 36 map reports have been completed as part of the Baltimore-Washington Urban Area Study; these 

reports are preceded by an asterisk in the list 

of references cited. 

This Circular summarizes some of the landand water-use problems in two counties typical 

of this urban study area-Montgomery and 

Prince Georges Counties-and describes how 

the map reports may be used to identify potential problem areas and assist in problem 

solving. Table 1 lists reports containing information on the geology, the hydrology, the 

mineral resources, and land-use planning in the 

Baltimore-Washington urban area. 

To be effective, county planning cannot be 

carried out totally independently of planning 

in adjacent jurisdictions, and local planning 

should be integrated with regional planning. A 

great variety of environmental planning takes 

place at all levels, as indicated by the list in 

table 2 of representative institutional users of 

geologic and hydrologic map reports. One planning proposal for the Washington metropolitan 

area calls for suburban growth along several 

major transportation corridors radiating outward from the urban core; low-density "greenbelt" wedges would remain between the corridors. Another regional planning solution to 

minimize suburban sprawl around Washington 

is to concentrate growth in outlying "New 

Towns," such as Columbia, Md., and Reston, Va. 

Solutions to other regional problems, such as 

meeting future water-supply needs, also depend on multijurisdictional planning. Basic 

knowledge of the physical environment can 

contribute to the solution of some of these complex regional planning problems. 

Perhaps the most serious environmental 

problem confronting rapidly urbanizing Montgomery and Prince Georges Counties today is 

the need to dispose of increasing volumes of 

solid and liquid wastes while protecting relatively clean surface waters and avoiding pollution of ground-water resources. Nearly as important to orderly and economic growth are the 

problems related to using sources of construe1. 
I 

I 

\ 

\ \ ,...,.---"'" 1 '---- I 

EXPLANATION \., 

,...oo 

1 :24,000-scale maps \.,_ ""00<7" 

c=="'""" ', River W 1:62,500-scale maps '--------\ 

' ' 

38'QQ•L_ ____ J_ ______________________ L_ ____________________ _L --------------------

0 10 20 MILES 

0 10 20 KILOMETERS 

FIGURE 1.-Index map showing areas mapped during the Baltimore-Washington Urban Area Study. 

2 
'rABLE 1.-Reports containing information on the geology, the hydrology, the mineral resources, and land-use 

planning in the Baltimore-Washington urban area 

[References preceded by an asterisk were prepared during the Baltimore-Washington Urban Area Study; they are interdisciplinary, 

and each contains a text describing how the geologic, hydrologic, or mineral-resource information can be applied to land-use planning] 

Gedlogy 1 

Cloos and Cooke, 1953 

Fisher, 1964; 1970 

*Froelich, 197 4 

*Froelich, 1975a, b, g, h 

Higgins and Fisher, 1971 

Hopson, 1964 

Johnston, 1964 

Matthews and others, 1961 

Nutter, 1975 

Reed and Jolly, 1963 

U.S. Geological Survey, 

1967a 

*Van Driel, 1975a/ b' 

*Withington and Froelich, 

1974a, b 

Cooke and Cloos, 1951 

Darton, 1947 

Glaser, 1971 

*Glaser, 1973 

Hack, 1955 

*Hack, 1977 

Hansen, 1968 

Jacobeen, 1972 

Johnston, 1964 

Kirby and others, 1967 

U.S. Geological Survey, 

1967b 

*Withington and Froelich, 

1974a, b 

Cloos and Cooke, 1953 

Cooke and Cloos, 1951 

Darton, 1947 

Fisher, 1970 

*Froelich, 1975c, e, f 

*Froelich and Hack, 1975 

Johnston, 1964 

Reed and J oily, 1963 

U.S. Geological Survey, 

1967a,b 

*Cleaves and others, 1974 

*Crowley and others, 1976 

Higgins and Fisher, 1971 

*Otton and others, 1975; 

1978 

U.S. Geological Survey, 

1967a,b 

Hydrology 2 Mineral resources 3 

Montgomery County, Md. 

Crooks and others, 

1967 

Dingman and Meyer, 

1954 

*Herb, 1976a 

Johnston, 1964; 1966 

*Mayer, 1977 

Nutt>er, 1974; 1975 

Nutter and Otton, 1969 

*Richardson, 1976a, c 

Cleaves, 1964 

Edwards, 1969 

Fisher, 1964 

*Froelich, 1975d 

Larrabee, 1969 

Pearre, 1961 

Reed and Reed, 1969 

Prince Georges County, Md. 

Crooks and others, 1967 

*Glaser, 1973 

Hansen, 1968 

*Herb, 1976b 

Johnston, 1964; 1966 

Mack, 1966 

Meyer, 1952 

Otton, 1955 

Papadopulos and others, 

1974 

*Richardson, 1976b, d 

Edwards, 1969 

Glaser, 1971 

*Glaser, 1973 

*Hack, 1976b 

Knechtel and· others, 

1961 

Pearre, 1961 

Washington, D.C. 

Johnston, 1964; 1966 

Papadopulos and others, 

1974 

Baltimore City and County, Md. 

Dingman and Ferguson, 

1956 

Nutter, 1974 

Nutter and Otton, 1969 

*Otton and others, 1975; 

1978 

8 

*Cleaves and others, 

1974 

Edwards, 1969 

Knechtel and others, 

1961 

*Ku:ff, 1975 

*Otton and others, 

1975; 1978 

Pearre, 1961 

Land-use planning 

Maryland-National Capital 

Park and Planning 

Commiss.ion, 1968-1972; 

1977 

*Stewart and Van Driel, 

1975 

*Van Driel, 1975c;" d' 

*Van Driel and Stewart, 1976 

*Glaser, 1973 

*Hack, 1976a; 1977 

*CleaVJes. and others, 1974 

*Otton and others, 1975; 

1978 
TABLE l.-Reports containing information on the geology, the hydrology, the mineral resources, and land-use 

planning in the Baltimore-Washington urban area-Continued 

Geology 1 Hydrology 2 Mineral resources 3 Land-use planning 

Other parts of the Baltimore-Washington urban area 

Glaser, 1971 

*Glas·er, 1973 

Hansen, 1968 

Higgins and Fisher, 1971 

Hopson, 1964 

J acobeen, 1972 

Nutter, 1974 

*Roen and Froelich, 1976; 

1978 

U.S. Geological Surve·y, 

1976a,b 

Dingman and Ferguson, 

1956 

Dingman and Meyer, 

1954 

*Glas,er, 1973 

Hansen, 1968 

Nutter, 1974 

Nutter and Otton, 1969 

Otton, 1955 

Papadopulos and others, 

1974 

Cleaves, 1964 

Edwards, 1969 

Glaser, 1971 

*Glaser, 1973 

Knechtel and others, 

1961 

Pearre, 1961 

*Glaser, 1973 

General references 

U.S. Soil Conservation 

Service, Engineering 

Division, 1975 

Geolo,gical Socie·ty of America, Committee on Environment and Public 

Policy, 1975 

Imhoff and others, 1978 

Leopold, 1968 

Leopold and others, 1971 

Robinson and Spieker, 1978 

Southeastern Wisconsin 

Regional Planning Commission, 1968 

Waananen and others., 1977 

William Spangle and Associates and others, 1976 

1 More extensive lists of references pertaini.ng to the geology of Montgomery County were given by Froelich (1975a, b, g, b); for references on Prince Georges County, see Hack (1977). 2 More extensive lists of references on the hydrology of Prince Georges County were given by Herb (1976b) and Richardson (1976b, 

d); for references on Montgomery County, see Herb (1976a) and Richardson (1967a, c). 3 A more extens1ve list of references on mineral resources of Prince Georges County was given by Hack (1976b); for references on Montgomery County, see Froelich (1975d). 4 Computer-generated map. 

tion materials-sand, gravel, and crushed stone 

-that are near the potential markets without 

degrading the environment; good planning 

would avoid the loss of these materials because 

of development over or near the deposits. 

Finally, the ultimate planning problem is the 

basis on which plans and plan-implementation 

decisions are made; we are learning that the 

expedient, short-term politico-economic choice 

that results in avoidable environmental damage 

is usually neither the best nor the only decision 

possible. 

Because both Montgomery and Prince 

Georges Counties are rapidly growing parts of 

the expanding Washington metropolitan area, 

typical urban-area problems common to both 

include the evaluation and selection of: 

1. Sites for waste treatment and disposal 

facilities. 

4 

2. Sites for water-supply storage and treatment facilities. 

3. Sources of construction materials. 

4. Land and water for parks and open-space 

preservation. 

5. Sites for conventional and nuclear power 

plants. 

Also, both counties need assessments of: 

1. Slope stability and landslide-prone areas. 

2. Foundation conditions, including areas 

where heavy construction would have to 

be limited. 

3. Tunneling conditions. 

4. Ground-water availability. 

5. Vaiiey-bottom land-use problems. 

6. Potential poiiution hazards, including 

solid waste, domestic sewage effluent, and 

siltation. 
TABLE 2.-Representative inBtitutional users of geologic and hydrologic map reports 

Planning Offices 

Mar;vl!"-J?-d-National Capital Park and Planning Commission, Planning Department, Silver Spring and Riverdale, Md. D!'VISIOn of Development Review Division of Environmental Planning Division of Research 

Montgomery County Government, Rockville, Md. Office of Planning and Capital Programming Office of Environmental Planning 

Office of Community and Economic Development 

Department of Architectural Services Department of Public Works Environmental Protection Agency 

Prince Georges County Government, Upper Marlboro and Riverdale, Md. Department of Program Planning and Economic Development 

Department of Public Works and Transportation Health Department Environmental Planning Division Metropolitan Washington Council of Governments, Washington, D.C. Department of Environmental Services Department of Health and Environmental Protection Maryland Department of State Planning, Baltimore, Md. 

Universities 

University of Maryland, College Park, Md. Department of Agronomy 

Department of Engineering 

George Washington University, Washington, D.C. University of the District of Columbia, Van Ness Campus, Department of Earth/Life Sciences, Washington, D.C. 

State and Federal Offices 

Maryland State Roads Commission, Bureau of Soils and Foundations, Brooklandville, Md. Maryland Geological Survey, The Johns Hopkins University, Baltimore, Md. U.S. Department of Agriculture, So] Conservation Service, College Park, Md., and Washington, D.C. U.S. National Park Service, Ecological Sciences Laboratory, Washington, D.C. U.S. Geological Survey, Towson, Md., and Reston, Va. U.S. Army Corps of Engineers, Baltimore, Md. 

Consulting Engineering and Industrial Firms 

Batelle Memorial Institute, Columbus, Ohio Bechtel Associates, Inc., Washington, D.C. CH2M Hill, Inc., Reston, Va., and Corvallis, Oreg. Columbia Gas System Service Corporation, Wilmington, Del. Commonwealth Associates, Inc., Jackson, Mich. Conlin and Gray Associates, Lancaster, Pa. Contee Sand and Gravel, Inc., Laurel, Md. Dames and Moore, Inc., Bethesda, Md. Inland Materials, Inc.,. Clinton, Md. Kamber Engineering Corp., Rockville, Md. Law Engineering Testing Company, McLean, Va. Pope, Evans and Robbins, Consulting Engineers, New York City, N.Y. Ralph M. Parsons and Associates, Washi,ngton, D.C. Schnabel Engineering Associates, Bethesda, Md. Wallace, McHarg, Roberts, and Todd, Philadelphia, Pa. Washington Metropolitan Area Transit Authority, Washington, D.C. Woodward-Clyde Associates, Rockville, Md. 

The environmental geologic and hydrologic 

maps of the two counties published during this 

study at the scale of 1:62,500 (1 in.= 1 mi) 

can be used in a rational assessment of many 

urban and regional problems related to land 

and water use (Froelich, 1974, 1975a, b, d, g, 

h; Hack, 1976a, b, 1977; Herb, 1976a, b; Mayer, 

1977; Richardson, 1976a-d). By using the maps 

separately and in combination, planners can 

take into consideration those natural factors 

that present opportunities for or limitations to 

many types of development. 

Most environmental problems in the bicounty 

area of Montgomery and Prince Georges Counties relate to the complex relationships between solid earth materials and water in 

natural processes. Therefore, to clarify these 

relationships and as a demonstration, the 

5 

U.S.G.S. in 1975 began working with the Maryland-National Capital Park and Planning Commission (MNCPPC) in the first cooperative 

effort of its kind to devise a computerized information system to meet the needs of a local 

planning program. The U.S.G.S. completed its 

contribution in late 1976, and the system has 

been operational since then. 

GEOLOGIC SETTING OF THE 

BALTIMORE-WASHINGTON URBAN AREA 

The physical features of Montgomery and 

Prince Georges Counties, Md., are representative of the entire Baltimore-Washington metropolitan area. The two counties lie across a small 

part of two distinctly different geologic provinces, the Piedmont to the northwest and the 

Atlantic Coastal Plain on the southeast. These 
provinces are separated by a line or zone known 

as the Fall Line (fig. 1), which closely approximates the boundary between the two counties. 

The Fall Line is the imaginary line drawn 

through the downstream location of falls or 

rapids that form a natural barrier to navigation on major streams; most of the major cities 

of the Atlantic Seaboard, including Baltimore 

and Washington, grew along the Fall Line. 

Almost all of Montgomery County is in the 

Piedmont, which is a terrain formed by the 

erosion of a thick blanket of weathered material 

that, in most places, covers hard, crystalline 

rocks (fig. 2) . Sedimentary rocks, chiefly shale, 

siltstone, and sandstone, are present in western Montgomery County. These rocks are overlain by a veneer of weathered material. Common construction problems in the Piedmont involve either hard rock or poorly drained soils 

that in places are present at, or just below, the 

land surface. Topography is gently rolling to 

hilly and, locally, hills are steep. Water problems involve flooding and waterlogging of 

valley bottoms, drainage at construction sites, 

pollution, and difficulties in developing adequate 

ground-water supplies. 

Prince Georges County is almost entirely in 

the Coastal Plain Province. The subsurface consists of layers of soft sedimentary materialclay, sand, silt, and gravel-that generally can 

be excavated by power shovels and other equipment. Clay soils and hardpan soils underlain by 

gravel and sand are present in large areas of 

the county and may cause severe construction 

problems. Development of adequate groundwater supplies from major sedimentary aquifers is possible. Firm bedrock is confined to a 

few small areas along stream valleys near the 

northern boundary. 

HYDROLOGIC CYCLE IN THE 

BALTIMORE-WASHINGTON URBAN AREA 

Among the processes that convert firm bedrock to loose surface materials having characteristic soil profiles are weathering and erosion, 

both of which function as a result of the hydrologic cycle. The hydrologic cycle is the continuous circulation of water from the land and 

sea to the atmosphere and back by precipitation, stream runoff, evaporation, and transpiration (fig. 3). The cycle is driven by the sun's 

energy. 

6 

Montgomery and Prince Georges Counties, 

Md., are in the humid temperate zone where the 

annual precipitation averages 43 in. (109 em). 

The precipitation is rather evenly distributed 

throughout the year, though August is the wettest month, and February is the driest. The 

ample precipitation in Maryland provides 

water to sustain the flow of the streams during 

most seasons and to replenish the soil moisture 

and the ground-water reservoirs (or aquifers) 

after periods of drought. The ground water in 

all Montgomery County and in all but the very 

deepest artesian aquifers in southern Prince 

Georges County is derived from precipitation. 

A few of these deep aquifers may contain some 

residual saline water remaining from invasions 

of ancient seas into the area. 

The distribution of precipitation as it reaches 

the land surface may be expressed quantitatively by the hydrologic equation, which is: 

P=ET+R±Saw 

where P=precipitation, ET=evapotranspiration, R=stream runoff, and Smv=change in 

ground-water storage. For the bicounty area, 

the quantities of water involved may be expressed in inches (centimeters) per year. These 

quantities are: 

43 =28 + 15+ 0 (inches) 

109 = 71 + 38 + 0 (centimeters) 

Water is added to and subtracted from the 

ground-water reservoirs (SGw) throughout 

seasonal and annual periods. This water may 

amount to several inches (centimeters) annually; however, during a long period of time, 

increments and decrements to the groundwater reservoirs must equal zero because the 

observed water table fluctuates by only 20 

feet (6 m), and the reservoirs do not overflow 

at the surface or become permanently dewatered. 

During dry periods, or during periods beginning 3-4 days after heavy precipitation, the 

flow of streams is sustained largely by groundwater discharge. Some of the flow in regulated 

streams may result from the release of water 

stored behind dams. On the average, 60 percent 

of the total stream runoff is derived from 

ground water, but this quantity varies in individual basins depending on geology, soil, topography, degree of urbanizatiton, and other less 

important factors. 
77°30' 

39 ° 00''-------l 

EXPLANATION 

( 

r:~ River bottom lands-alluvium 

~ @iJ and terrace deposits c 

s 

~ ~--2--j Upland deposits (gravel and sand) 

(.) 

c ·a co-N 

·.::: 0 g .o __ 

E-o co cocO.. 

UCO'-

Q) Q) 

.... ~ 

c... .2 

Thinly layered marine clay, 

sand,and marl 

Complex ancient river deposits 

of clay, sand,and gravel 

Sandstone, shale, and diabase 

(traprock 5d) 

38°45''----t 

( 

16-l Nonconsolidated weathered material 

~- ~ 

1 

(saprolite) as much as 180 feet (55 m) thick 

Crystalline bedrock with thin soil cover 

77° 00' 

76°45' 

0 

10 KILOMETERS 

FIGURE 2.-Generalized geologic map of Montgomery and Prince Georges Counties, Maryland. Modified from 

Froelich (1975a, g) and Hack (1977). 

7 
PRECIPITATION 

PIEDMONT 

CLARKSBURG 

WEATHERED ZONE 

~r' II 

$' SILVER SPRING 

#: l:l 

w 

z 

::J 

....J 

....J 

;t 

COLLEGE PARK 

f-

~ 

::;: 

t t ~ 

~ z 

0 

if 

~I 

z 

0 

~ a: 

fJJ 

z 

g 

COASTAL PLAIN 

UPPER MARLBORO 

FIGURE 3.-Diagrammatic seetion from Clarksburg to the Patuxent River in the Bal,timore-Wa,shington urban 

area showing major geolog,ic features and the hydrologic cycle. 

Figure 4 shows graphically, by monthly averages, the water budget of the Patuxent River 

basin above the Unity gaging station (fig. 1). 

Above the station, the river drains a 35-mi2 

(90 km2 ) area underlain by metamorphic and 

igneous rocks. Figure 4 shows that both precipitation and runoff do not range widely during an average year. It also shows that the 

ground-water reservoirs are recharged mostly 

during the period from mid-September through 

March. The greatest loss of water from the 

basin by evapotranspiration occurs during the 

period from early April to mid-September, the 

8 

growing season and the period of warm temperatures. 

THE USE OF l\fAP REPORTS FOR THE 

APPRAISAL OF SOl\fE COlVIlVION LANDUSE PROBLElVIS 

The map reports at 1: 62,500 scale can be 

used as an aid in making a wide range of planning decisions. Some examples of this applicability are described below. 

SLOPE-STABILITY PROBLEMS 

As used here, slope stability refers to the 

susceptibility of natural slopes to failure by 
8,--,--.---.--,---.--,---.--,---.--,---,--,20 

6 15 

Output EXPLANATION 

0: (evapotranspiration 0: 

w L.U plus runoff) t- t- <( 

~ ~ 

u. u. 

0 0 Ground-water storage 4 10 (/) (/) 

w 0: 

L.U D :I: t- u L.U 

~ ~ 

i= 

z Deficiency w 

u 

5 

o~~---r--+-~r--+--~--~~--~--~--r-~o 

J F M AM J J AS 0 N D 

Precipitation =42.8 inches (109 em) 

Runoff =15.0 inches (38 em) 

Evapotranspiration =27.8 inches (71 em) 

FIGURE 4.-Water budget for the Patuxent River basin above the Unity gaging station. 

landslides, creep, or rockfalls as well as the 

stability of excavations in hillsides and trench 

walls. A county-wide slope map of Montgomery 

County was prepared by the MNCPPC in 1977 

as an aid to regional planning. The map is the 

same scale (1: 62,500) as the U.S.G.S. maps 

(Froelich, 1974, 1975a, b, d, g, h; Hack, 1976a, 

b, 1977; Herb, 1976a, b; Mayer, 1977; Richardson, 1976a-d) and can be overlain on the surface-materials map (I-920-A by Froelich, 

1975g) to evaluate slope stability. For example, 

by overlaying areas of slopes greater than 25 

percent on unit 4, which includes Coastal Plain 

clays (I-920-A), landslide-prone areas are defined. Such areas are particularly likely to fail 

where natural slopes are disturbed or cut during construction. 

A sharp division is present between bedrock 

and overburden materials in Montgomery 

9 

County (fig. 2). The bedrock (fig. 2, unit 7) is 

mostly hard rock that can be excavated or 

moved only by blasting. The overburden is 

loos~ enough to be excavated with power equipment. In m.ost parts of the country, this material (saprolite, fig. 2, unit 6) is derived from 

the bedrock by weathering. It averages 45 feet 

(13.6 m) in thickness and is thicker on the 

ridge tops than in the valleys. Other kinds of 

surficial overburden, such as river alluvium 

and terrace deposits are also present (fig. 5). 

The depth of this material is shown on the 

thickness-of-overburden map (I-920-B by 

Froelich, 1975h), and its characteristics are 

shown on the surface-materials map (I-920-

A). Natural landslides, creep, and rockfalls 

may take place in Montgomery County on some 

extraordinarily steep slopes, but only rarely 

are they solely a consequence of heavy rain. 
MAP VIEW 

FIGURE 5.-Block diagram of hypothetical area in Montgomery County showing examples of common surface 

materials that overlie bedrock. 

The problem is quite different in Prince 

Georges County, for hard bedrock is near the 

surface only in ravines and valleys in the northwestern part of the county near the Montgomery County line (fig. 2) . In most of Prince 

Georges County, the earth materials are usually 

soft enough to be readily excavated by power 

shovels. Differences exist, however, in degree 

of consolidation and strength characteristics of 

the material. Overconsolidated material (sediments previously compressed by thick overburden, subsequently eroded away) is common. 

Unfortunately, data are not available to show 

the depth to overconsolidated material. In general, however, overconsolidated material is 

present in the older sediments such as the 

sand, gravel, silt, and clay of unit 4 and the 

sand and sandy clay of unit 3 (fig. 2). In both 

units, the overconsolidated material is generally overlain by a blanket of much weaker 

material that may range from 5 to 20 feet 

(1.7-6 m) in thickness. In places, this weaker 

material is soil derived by weathering from the 

material below. In places, it is windblown material mostly locally derived from underlying 

sediments during former periods when the 

climate was drier than now. Unit 2 (fig. 2) is 

the upland deposits, which are ancient river 

gravel, sand, and silt; unit 2 has never been 

compressed by a thick overburden and thus 

is not overconsolidated. 

Clay, some of it having a long history of instability when disturbed by excavation or loading, is present in Prince Georges County. Clay 

is particularly common in unit 4 (fig. 2) ; but 

in unit 3, thin clay layers are present at various 

depths. Clay layers in both units have caused 

stability problems. These problems include 

10 
FIGURE 6.-Landslide m Cretaceous clay of unit 4 (fig. 2), s·outheast Washington, D.C., adjacent to Prince 

Georges County line. 

creep and natural sliding on steep slopes (see 

fig. 6) as well as difficulty in compacting the 

clay because of the presence of silty material. 

The available data on the location and relative stability of the various kinds of material 

that may be found in Prince Georges County 

are shown on map MF-768-B (Hack, 1976a) 

and map I-1004 (Hack, 1977). These maps are 

best used for preliminary site evaluation and 

selection. For example, where the contour lines 

are close together, steep slopes are indicated. 

Where steep slopes coincide with a clay bed, 

slope stability is low. Where contour lines are 

relatively widely spaced, slopes are gentle, and 

gently sloping areas underlain by sand or upland gravel are relatively stable. 

FOUNDATION CONDITIONS 

A wide range in foundation conditions prevails in the bicounty area. These conditions are 

classified according to ( 1) the depth of material that can be excavated without blasting, 

(2) the swelling properties and strength and 

compressibility of the consolidated material, 

and (3) the surface and shallow subsurface 

drainage conditions. 

The thickness-of-overburden map (I-920-B 

by Froelich, 1975h) can be used to judge the 

approximate amount of overburden in various 

regions of Montgomery County. Where the 

overburden is thick, the character of the foundation material can be judged from the surface-materials map (I-920-A by Froelich, 

1975g) . Most of Montgomery County is covered by weathered rock overburden (saprolite, 

fig. 2, unit 6), which, in general, provides good 

foundation conditions for homes and light 

structures. The saprolite can be readily excavated without blasting. However, in places, 

small or isolated bodies of hard rock may be at 

shallow depth, and such bodies are not indicated 

on maps I-920-A, B. 

11 

In Montgomery County, bedrock crops out 

or is shallow in more than one-third of the 

area (fig. 2, unit 7) . Where bedrock is shallow 

or exposed, exploration by means of borings is 

necessary at construction sites to avoid excessive rock excavation and blasting. The bedrock 
map (I-920-D by Froelich, 1975a) furnishes 

information about the strength and character 

of near-surface bedrock. One bedrock unit, 

serpentinite, is especially noteworthy because it 

has caused many construction problems in the 

county. It generally is found close to the surface and is unusually difficult to excavate. 

Furthermore, serpentinite is nearly impervious 

to water so that drainage through it is poor. 

The approximate depth to the water table in 

Montgomery County is shown in U.S.G.S. openfile report 76-881 (Richardson, 1976a). Information on the depth to the water table and its 

cyclical fluctuations is of interest to engineers, 

planners, and others considering land use and 

foundation conditions. Knowledge of the extent and distribution of areas where the water 

table is shallow (within 10 feet (3 m) of the 

land surface) is critical in planning: ( 1) highway construction, (2) activities involving extensive earthmoving, and (3) large structures 

having deep foundations. Special engineering 

treatment may be needed in foundations periodically subject to wetting and drying. Upland, 

interstream areas where the water table is 

more than 35 feet (10.6 m) below the land surface, if moderately well drained and underlain 

by permeable soils, may be suitable for large 

structures requiring deep foundations. U.S.G.S. 

open-file report 76-882 (Richardson, 1976c) on 

the availability of ground water in Montgomery 

County includes a hydrograph showing that the 

water level in a 58-foot (17.5-m-) -deep observation well near Damascus fluctuated throughout a range of 20 feet (6 m) during the 5-year 

period indicated on the graph. Similar fluctuations may be expected in other bedrock wells in 

Montgomery County and would affect deep 

foundations. 

More than 95 percent of Prince Georges 

County is underlain by easily excavated material, though earth materials are generally 

compacted at depths greater than 10-20 feet 

(3-6 m) below the surface. Locally, hard bedrock is near the surface only in valleys along 

the Montgomery County line, and, except for 

small areas of cemented sand that exist in the 

Aquia Formation (map I-1004 by Hack, 1977), 

rock excavation is not a problem. 

Prince Georges County contains extensive 

areas underlain by clay, which provides poor 

foundation conditions (fig. 2, units 3 and 4). 

Map MF-768-B delineates areas underlain by 

a kind of clay (Hack, 1976a, unit 4) that has a 

particularly bad record for sliding and creep. 

It does not have swelling properties at all 

localities; nevertheless, it becomes unstable 

when wet, especially on sloping ground. In 

places, it is interbedded with layers of porous 

sand; saturation of these sand layers increases 

the landslide hazard. Other clay layers interbedded with sand and gravel are in unit 4 of 

figure 2 (Hack, 1976a, unit 4 + 1) and may contain montmorillonite, a clay mineral that swells 

when wet and shrinks when dry. The clays are 

commonly covered on the surface by several 

feet (a meter) of soil material overlying colluvium that contains transported sand or sand 

and gravel so that the clay may not be readily 

visible and can be found only by drilling or 

augering. Caution should be used in planning 

construction in all areas where clay is present. 

In some places in Prince Georges County, 

fuller's earth (diatomite) is mixed with swelling clay (Hack, 1976a, unit 2). Diatomite, because of its composition and silty texture, is 

difficult to compact. 

The approximate depth to the water table in 

Prince Georges County is shown in U.S.G.S. 

open-file report 76-194 (Richardson, 1976b). 

In Prince Georges County, the water table is 

commonly within 10 feet (3m) of the land surface chiefly along stream valleys, and extensive 

areas along the Patuxent and Potomac Rivers 

are in this category. Although no hydrographs 

were given by Richardson (1976b) for Prince 

Georges County, data from nearby areas indicate that the water table normally fluctuates 

only a few feet (a meter) during an annual 

cycle. 

Special foundation conditions are present in 

unit 2 (fig. 2). This unit contains a hardpan 

layer in the soil 2-3 feet (0.7-1 m) below the 

surface. This layer is several feet (a meter) 

thick and is not pentrated by tree roots. It is 

nearly impervious to water so that in winter 

and in periods of heavy rain, surface drainage 

is poor, and some areas of flat ground are 

flooded. VVhere large structures that require 

deep excavations are built, the hardpan layer 

should not create foundation problems, for it is 

underlain by loamy sand and sand and gravel. 

Surface drainage around structures, however, 

is necessary. 

12 
TUNNELING CONDITIONS 

During the period of the Baltimore-Washington Urban Area Study, the Washington 

Metropolitan Area Transit Authority began 

construction of a municipal subway (METRO). 

Radiating out from the Nation's Capital like 

spokes of a wheel, the underground tunnel system traverses Piedmont terrain to the north 

and west and the Coastal Plain to the south 

and east. Much of the experience gained during 

tunneling in Washington may be applicable to 

other major cities along the Fall Line zone, 

such as Baltimore, Md., and Richmond, Va. 

Only generalized aspects of the engineering 

geology of this tunnel are mentioned briefly 

here. 

The most important aspect of tunneling in 

the Piedmont is the character and position of 

the contact between soft, clay-rich weathered 

material (saprolite) and the underlying hard, 

fresh bedrock. Physical properties of the 

weathered material differ radically from those 

of unweathered rocks; the weathered material 

is much weaker, more compressible, and more 

porous and permeable. Tunnels driven through 

either soft weathered material or hard bedrock 

seldom have difficult excavation or support 

problems. Tunnel-boring machines (moles) 

are routinely used for excavating bedrock and 

achieve rapid economical rates in sound bedrock. Local problems with fractured, jointed, 

or faulted bedrock of low strength at contacts 

between contrasting rock types, possibly accompanied by an influx of water, may require 

special shoring, lining, and grouting techniques. However, severe excavation problems 

with attendant high costs are invariably encountered in mixed-face tunnels, where the 

upper part of the bore is in soft weathered 

material and the lower part is in hard bedrock. 

As this crucial contact is commonly irregular, 

the accurate location of this boundary by means 

of geologic mapping and a detailed core-drilling program in advance of tunneling is critically important. Maps showing thickness of 

overburden [I-920-B (Froelich, 1975h) ; 

U.S.G.S. open-file reports 75-418 (Van Driel, 

1975a) and 75-538 (Froelich, 1975f)] and contours on the base of saprolite [I-920-C (Froelich, 1975b), U.S.G.S. open-file report 75-539 

(Froelich, 1975c)] are useful in preliminary 

design stages to delineate potential problem 

areas for various tunnel depths. 

Tunneling or cut-and-cover excavation in the 

nonconsolidated sediments of the Coastal Plain 

presents different engineering problems. The 

oldest sediments are mainly interbedded sands 

and clays of the Potomac Group. They are generally almost ideal tunneling materials that are 

readily excavated and stand well in steep cuts. 

Minor problems relate to swelling and shrinking of stiff clay (montmorillonite), shear zones 

containing plastic clay, spalling and heaving 

of overconsolidated clay, and dewatering of 

porous sand layers. However, the Potomac sediments are overlain by a sequence of much 

younger gravel, sand, silt, clay, and peat beds 

that are generally weak, are commonly watersaturated, and are extremely variable in vertical and lateral distribution. Some of the 

porous and permeable gravel in contact with 

underlying clay is a source of concentrated 

ground-water flow that has caused severe instability during excavation. Because of the erratic distribution of porous gravel deposits, it 

is very difficult to predict the location and magnitude of potential excavation problems or the 

necessity for dewatering of aquifers. Careful 

geologic mapping and a comprehensive drilling 

and coring program in advance of excavation 

is usually successful in anticipating these subsurface problems. 

The Fall Line zone contains most of the problems discussed above that are found in mixedface tunneling operations in the Piedmont and 

Coastal Plain. These problems include irregular surfaces of hard rock beneath soft, watersaturated, porous, gravelly sand deposits of the 

Coastal Plain; erratically distributed lenses of 

plastic clay; and highly variable weak and 

water-saturated sediments near the surface. 

The Fall Line zone obviously requires the most 

careful and intense geologic and engineering 

fieldwork in advance of tunneling. 

GROUND-WATER AVAILABILITY 

MONTGOMERY COUNTY 

The availability of ground water in Montgomery County ranges from poor to fair because most of the county is underlain by dense 

metamorphic and igneous rocks that are relatively low-yielding aquifers. Ground water is 

present in these rocks chiefly in a thin zone at 

the base of the weathered material (saprolite) 

and in crevices and fractures in the underlying 

bedrock. Most of the crystalline rocks yield 

13 
domestic supplies of at least a few gallons per 

minute (gpm), sufficient for single-family 

residences. Only where the rocks are intensely 

fractured or deeply weathered can ground 

water be found in larger quantites. Because of 

fluctuations of the water table, some shallow 

wells completed in wet years may go dry during droughts. 

A veneer of Coastal Plain sediments is present over the dense rocks mainly in a belt a few 

miles wide near the Prince Georges County 

line (fig. 2). Throughout most of Maryland, 

Coastal Plain deposits contain major aquifers, 

but along the eastern edge of Montgomery 

County, these sediments either lie above the 

zone of saturation or are too thin to be significant aquifers. Hence, most wells in this belt 

are drilled into the underlying crystalline rocks 

in order to obtain adequate domestic supplies. 

U.S.G.S. open-file report 76-882 (Richardson, 1976c) provides information on the relative availability of ground water in Montgomery County. On this map, the county has 

been divided into six major hydrogeologic units, 

chiefly on the basis of the variability of well 

yields from various rock types. The yields of 

474 wells were grouped into small (0-5 gpm 

(0-0.315 L/s), moderate (6-25 gpm (0.38-

1.6 L/s), or large (more than 25 gpm (1.6 

L/s)) yields according to aquifer rock type. 

The various groupings are identified on Richardson's (1976c) map as hydrogeologic units 

1 through 6. Unit 1, underlain by gneiss and 

granite, has the greatest percentage (about 30 

percent) of wells having ~ported yields in excess of 25 gpm (1.6 Lfs}. 

Hydrogeologic unit 2, underlain by schist, 

has the second greatest percentage of wells 

having large yields (about 25 percent). The 

town of Laytonsville is in the center of a large 

area designated as hydrogeologic unit 2. Thus, 

for example, a small industry or commercial 

establishment attempting to develop a groundwater supply of 50 gpm (3.15 L/s) near Laytonsville would find U.S.G.S. open-file report 

7€·-·882 useful in evaluating its ·chances for obtaining the required supply. 

Consolidated sedimentary rocks in the western part of the county compose hydrogeologic 

unit 3, which occupies a large area centered 

around Poolesville. Unit 3, underlain mainly by 

Triassic sedimentary rocks, offers the best opportunity to develop moderate to large sus14 

tained yields of ground water in Montgomery 

County. Nutter stated (1975, p. 1) "Groundwater supplies sufficient for most commercial 

and light industrial use can be developed under 

favorable hydrogeologic conditions." He pointed out that water is stored in and transmitted 

through joints, faults, and bedding-plane partings in the sedimentary rocks and that rock 

type, well depth, and topographic position are 

other important factors bearing on yield. Although yields of only 17 wells ( 15 percent) of 

the 110 wells in unit 3 exceed 25 gpm (1.6 

L/ s) , most of the wells used in the compilation (Richardson, 1976c) are domestic wells 

probably not pumped at their maximum capacity. As shown in I-920-D (Froelich, 1975a), 

the sandstone and siltstone bedrock may be 

greater than 3,300 feet (1,000 m) thick along 

the western border of the county. Future deep 

wells may tap water-yielding fractured sandstones not heretofore penetrated by the relatively shallow domestic wells in the area. 

PRINCE GEOR:GES COUNTY 

The availability of ground water in Prince 

Georges County ranges from moderate (25 

gpm (1.6 L/s)) to excellent (more than 200 

gpm (12.6 L/s)). Except for a few small areas 

of crystalline rocks along the north and west 

boundaries, the county is underlain by Coastal 

Plain sediments (fig. 2). The extensive sediments in the county contain four major aquifers-in ascending order, the Patuxent, Patapsco, Magothy, and Aquia. These aquifers 

are chiefly sheetlike layers of sand which slope 

to the southeast where they are found at progressively greater depths (see fig. 3). 

The oldest and northernmost aquifer, the Patuxent, has been tapped as a source of ground 

water throughout a large part of northern and 

western Prince Georges County. Map A in 

U.S.G.S. open-file report 76-197 (Richardson, 

1976d) provides information on the yields of 

wells in the Patuxent aquifer and on the iron 

concentration and hardness of the wate!". The 

map sJ:tows, by means of contours, the altitude 

above or below sea level to which wells must 

be drilled to obtain water from this aquifer. 

Map A of U.S.G.S. open-file report 76-197 

should be useful in situations such as a government agency wishing to obtain 100 gpm 

(6.3 L/s) for a proposed research facility near 

Greenbelt (fig. 2). The minus-100-foot contour 
on map A passes through Greenbelt, thus 

showing the altitude below sea level of the top 

of the Patuxent aquifer. A nearby well, Cd23, 

at the Goddard Space Center (see map A, 

Richardson, 1976d), yielded 162 gpm (10.22 

L/s) from this aquifer. Well Cd23 was 6 in. 

(15 em) in diameter, 444 feet (135 m) deep, 

and had 17 feet (5 m) of well screen in it. Map 

A also shows that the iron content of the wate,r 

may be expected to be greater than 1.0 mg/L 

and that the hardness of the water is in the 

range of 0-60 mg /L. Iron concentrations in 

excess of 0.3 mg/L may cause staining of 

fabrics and plumbing fixtures. Hence, the potential user of this water should be prepared to 

install iron-removal equipment in the water 

system. 

Information similar to that given in map A 

and the above example for the Patuxent is 

given in maps B, C, and D of U.S.G.S. open-file 

report 76-197 (Richardson, 1976d) for the 

other three aquifers-the Patapsco, Magothy, 

and Aquia. As the yields of individual wells are 

related to regional declines in artesian head 

and to well spacing, ground-water availability 

in the Coastal Plain is better evaluated in terms 

of aquifers than in terms of individual well 

yields. The best technique to appraise a Coastal 

Plain aquifer is to design a digital-computer 

model that incorporates all known geologic and 

hydrologic data. A preliminary model study of 

Coastal Plain aquifers in the Washington, D.C., 

area, including Prince Georges County, was 

made to estimate the water-supply potential 

(Papadopulos and others, 1974). The study indicated that an additional 110 million gpd (gallons per day) could be withdrawn within 30 mi 

( 48 km) of Washington on an emergency basis. 

Such large-scale pumpage from the four Coastal Plain aquifers within or outside the county 

would appreciably lower the ground-water level 

and reduce ground-water availability within the 

county. 

CONSTRUCTION MATERIALS AND 

MINERAL RESOURCES 

The chief mineral resources produced in the 

bicounty area are used primarily as construction materials and highway fill. They include 

crushed stone and building stone from the crystalline Piedmont rocks of Montgomery County 

and sand, gravel, and clay from the Coastal 

15 

Plain sediments of Prince Georges County 

(fig. 2). 

Critical resources necessary for future construction are crushed stone and sand and gravel 

that are found at or near the surface (fig. 7). 

To be most economical, they must also be close 

to the area of use. Fortunately, large reserves 

of these necessary construction materials remain in the bicounty area, but new sources may 

be required to fulfill future requirements as 

urbanization continues. Many valuable nearsurface deposits have already been lost because 

they have been covered by buildings, and streets, 

and more will be lost unless such deposits are 

recognized and preserved by land-use planning 

and plan implementation. Serious consideration 

should be given to the extraction of these resources prior to urban development. Their extraction can be considered an interim use. After 

extraction of construction materials, the land 

can usually be reclaimed for agriculture, recreation, building sites, and in some places, waste 

disposal. Careful advance planning for reclamation of a proposed site prior to extraction and 

adherence to the plan can minimize environmental damage. 

CRUSHED STONE.-Severallarge deposits 

of rock-serpentinite (fig. 2, unit 7) and 

diabase (fig. 2, unit 5d) -suitable for crushed 

stone are present in the Piedmont of westcentral Montgomery County (I-920-E by Froelich, 1975d). These rocks make aggregate of 

excellent quality because of their toughness, 

uniform texture, and resistance to chemical 

weathering. 

Large quantities of crushed serpentinite were 

produced in 1976 from the major quarry west 

of Rockville (fig. 8) ; the material was used as 

binder and filler for highways, as road metal, 

and as aggregate in concrete (Larrabee, 1969, 

p. 29) . Large reserves of this deposit remain, 

but the serpentinite is rapidly being encroached 

on and covered by detached homes and public 

buildings. 

A large diabase body exposed at land surface 

near Boyds (fig. 2) contains rock similar to 

that extensively quarried nearby in Virginia 

for crushed stone. It is the last major potential 

source of crushed stone of that type in the hicounty area. A 1-mi2 (2.6-km2 ) area, if excavated to a depth of 50 feet (15m), would yield 

about 130 million tons, sufficient for 30 years 

supply at the present rate of consumption. 
WEST 

MONTGOMERY COUNTY 

TRIASSIC LOWLAND PIEDMONT 

EAST 

PRINCE GEORGES COUNTY 

FALL LINE 

~+= 

Sand and gravel 

pits in Upland 

gravel and 

Potomac Group 

COASTAL PLAIN ____ _ 

Alluvial and 

terrace sand 

and gravel 

Shale and residuum 

for tile and bricks 

Serpentinite quarry 

for crushed stone Gneiss schist quarry 

for building stone, l 

flagstone and rip-rap 

FIGURE 7.-Diagrammatic section across Montgomery and Prince Georges Counties showing occurrence of construction materials and rock and mineral resources. 

BUILDING STONE.-Several rock quarries 

in jointed schist and gneiss (fig. 2, unit 7) west 

of Bethesda in Montgomery County were producing flagstone, building stone, veneer, slate, 

fill, and riprap for local use in 1976 (I-920-E 

by Froelich, 1975d). Extensive reserves of similar rock remain at shallow depth near the 

Potomac River, but most of the accessible sites 

are now used as streamside parks or residential 

areas. Other accessible deposits that have not 

been commercially evaluated are present in the 

same outcrop belt along the Patuxent River in 

the more rural, northern part of the county. In 

most of the area, however, building-stone needs 

are n1et by importation at increased cost. Local 

building-stone availability can be assessed by 

using three maps: I-920-E (Froelich, 1975d) 

shows where building stone was formerly quarried; by overlaying this map on I-920-D (Froelich, 1975a), belts of rock similar to that quarried can be defined; by overlaying the favorable 

belts on I-920-B (Froelich, 1975h), specific 

16 

areas of shallow overburden can be delineated, 

indicating accessibility of the rock. Once the 

areas where the building stone is accessible are 

identified, decisions to open quarries depend on 

nongeologic factors. 

SAND AND GRA VEL.-Sand and gravel 

constitute the principal mineral resources of 

Prince Georges County; such resources are 

mostly depleted or preempted in Montgomery County. Sand and gravel are present in 

extensive bedded deposits in the Coastal Plain 

in the northern part of Prince Georges County. 

Large amounts of gravel and sand have been, 

and still are being, extracted from ma~y shallow pits (fig. 9). Thick deposits of mediumand coarse-grained quartz sand, as well as 

lenses and layers of poorly sorted pebble gravel 

and sand, are common. 

Extensive sand and gravel resources are 

present in the upland deposits in a large triangular area in the southern half of Prince 

Georges County. The sand and gravel are 
FIGURE 8.-Aerial view of quarry in serpentinite west of Rockville, Montgomery County. 

present mostly in a shallow sheetlike layer 20 

to 40 feet (6-12 m) thick that blankets a 

plateaulike surface. The texture of these deposits is uneven; the gravel is present in lenticular bars or channels intermixed with sand. 

In general, the material is finer grained upwards, and 10-15 feet (3-4.5 m) of fine sand 

and silt is near the surface (fig. 10). The base 

of the sand and gravel sheet is irregular but 

forms a sharp boundary with underlying very 

fine sand. 

Large quantities of sand and gravel are 

present in alluvial flood plains and adjacent 

terrace deposits of the principal streams, especially the Potomac and Patuxent Rivers. Some 

of these deposits have been used as sources of 

construction material, but their extraction 

presents a potential sediment-pollution hazard; 

furthermore, the alluvial deposits are subject 

to flooding. Gravel is also dredged from shoals 

in the Potomac River that are ancient drowned 

terrace deposits. 

CLAY.-Clay of various kinds is present in 

many geologic units throughout Prince Georges 

County but is sparse in Montgomery County, 

17 

except in saprolite on crystalline rocks or in 

residuum on shale. Clay is present in the Coastal Plain .of Prince Georges County as lenslike 

bodies interlayered with sand and gravel. 

Thick, massive beds of clay (kaolinite and 

illite) are in a belt passing through Muirkirk 

(fig. 2) where it was extracted from pits for 

many years; it is used to make brick, tile, and 

other ceramics. To the east, the clay is commonly mixed with layers and lenses of sand, 

and to the south near the Potomac River, the 

clay commonly contains more than 20 percent 

montmorillonite, making it unsuitable as brick 

or ceramic material. 

A thin persistent clay layer about 10 to 30 

feet (3-9 m) thick, known as the Marlboro 

Clay, crops out or occurs near the land surface 

in parts of the southern half of Prince Georges 

County. In general, the clay contains thin 

layers of silt and is moderately plastic. According to Glaser (1971, p. 53- 55), it has potential 

use as a ceramic material suitable for face 

brick and structural tile. 

Fresh and weathered shale in southwestern 

Montgomery County may be suitable for light-
FIGURE 9.-Aerial view of gravel pits, northern Prince Georges County. 

weight aggregate or for terra cotta pipe and 

tile products (Edwards, 1969, p. 24). The shale 

is common northwest of Seneca, but it is generally silty, locally calcareous, and interbedded 

with siltstone and sandstone. 

DRAINAGE BASINS, LAND-USE PLANNING, AND ZONING 

A drainage basin is a landform that includes 

all the area contributing runoff to a stream; 

it is bounded by drainage divides that separate 

the drainage of adjacent basins. A modern approach to comprehensive land-use planning in 

the bicounty area utilizes the drainage basin as 

a basic reference unit to which earth science 

and other data are related. The drainage basin 

map of Montgomery County (Mayer, 1977) 

provides a natural framework for the inventory of factors that are critical to urban development in a given basin. For example, 

urbanization of the headwaters of a stream can 

18 

degrade the flood plain and stream channel 

throughout its length, whereas similar development near the mouth has less effect on the system (U.S. Soil Conserv. Service, 1975). The 

MNCPPC is exploring the possibility of comprehensive land-use planning and zoning that 

will encourage development in those parts of 

the drainage basin that are least sensitive to 

environmental disruption so that the adverse 

effects of urbanization on the basin will be 

minimized. 

PROBLEMS OF VALLEY-BOTTOM LANDS 

Valley-bottom lands have special problems relating to land use and urbanization. Flooding 

and high water tables make valley bottoms unfit sites for any type of building that might 

obstruct the floodway, for underground sewage disposal, and for sanitary landfills. The 

valley-bottom soils are poorly suitable for use 

in road subgrades and road fill. 
FIGURE 10.-Coarse sand a nd gravel overlain by fine sand and silt exposed in a pit in southeastern Prince 

Georges County. 

Flooding is a natural characteristic of all 

streams. A flood takes place when more water 

comes down the stream than can be carried 

within the stream channel, and the water spills 

out over the valley floor or flood plain. Although a stream may flood only a few times a 

year, a large quantity of water is transported 

in a short time. Floods can cause economic loss 

and can be a severe hazard to life and property. 

They are, however, a significant element in the 

normal runoff component of the hydrologic 

cycle. 

Flooding is a problem common to the valleybottom lands in Montgomery and Prince 

Georges Counties. Severe floods have occurred 

many times in the area, and local damage has 

been extensive. U.S.G.S. open-file reports 76-

884 and 76-178 (maps by Herb (1976a, b) 

showing availability of hydrologic data) show 

t he extent of flood-prone areas along the major 

streams in Montgomery County and Prince 

19 

Georges County, respectively. In addition to 

these maps at a scale of 1:62,500, both counties 

are completely covered by larger scale U.S.G.S. 

maps showing flood-prone areas at a scale of 

1:24,000; the larger scale maps are available 

on request from the District Chief, Water Resources Division, U.S.G.S., 8600 La Salle Road, 

Towson, Md. 21204. 

The water table is shallow, 10 feet (3 m) or 

less, nearly everywhere along the valley-bottom lands in the bicounty area (Richardson, 

1976b, c). Swamp conditions persist for most 

of the year in some localities; elsewhere, drainage ditches have been dug to lower the water 

table and render the land usable for farming 

or grazing. 

Of course, bottom lands are subject to a 

fl uctuating water table, which rises to the surface during wet periods and falls during 

droughts. These lands are generally poor sites 
for sanitary landfills or for soil-absorption 

sewage-disposal systems. At many places, discharging ground water may mix with landfill 

leachate or sewage effluent and contaminate 

surface waters. Where sanitary landfills are 

placed in flood plains, the landfill material can 

physically impede the flow of water during 

periods of overbank flow and then increase the 

flood hazards in upstream areas. Where ground 

water enters an aquifer, leachate or effluent 

may also enter the aquifer and pollute it. Soilabsorption sewage-disposal systems constructed 

during dry periods when the water table is below the bottom of the field may function satisfactorily during dry periods. During wet periods, the water table will rise, rendering the 

system inoperable and resulting in mixing the 

effluent directly into the surface or ground 

water. 

Obstructions on the flood plain such as undersized bridges, culverts, or approach embankments, or commercial, indvstrial, or residential buildings may reduce the cross-sectional 

area and raise the flood stage. Concentrated 

urban development may impede flow sufficiently to raise the flood stage substantially and 

to cause increased damage by inundation 

(Waananen and others, 1977, p. 14). 

The valley-bottom lands in both counties are 

nearly everywhere underlain by alluvial deposits covered by soils of several series. Matthews, Compy, and Johnson (1961, table 6) 

and Kirby, Matthews, and Bailey (1967, tables 

8, 9) indicated that these soils are poorly suitable for road subgrades and for road fill. 

SANITARY-LANDFILL SITES 

Large quantities of solid waste are being 

generated by the urbanized counties adjacent 

to Washington, D.C. To dispose of this material in "garbage dumps" is no longer acceptable, and currently (1976) solid waste is put 

in engineered and designed "sanitary" landfills (fig. 11). Sanitary landfills differ from 

garbage dumps in that the solid waste, consisting of trash and garbage, is deposited in 

unit cells, is compacted by a bulldozer, and is 

covered at the end of each day by a thin layer 

(about 6 in. (15 em)) of soil. This disposal 

method is a substantial improvement over the 

older method, but potential hazards of polluting surface and ground-water supplies by 

leachate persist. The composition of the 

leachate is related to the nature of the materials in the fill and is generated by their 

reacting with infiltrating precipitation. In 

humid areas such as Maryland, some leachate 

is generated at all landfills. 

Precipitation on the surface infiltrating into 

the landfill either emerges as flow into a ditch 

or stream or enters the underlying groundwater reservoir. It is desirable to reduce the 

quantity of leachate formed and to control or 

contain leachate that is unavoidably formed. 

The amount of leachate formed can be reduced 

somewhat by covering the landfill with material sufficiently impervious to reduce or 

eliminate water infiltration. The base of the 

landfill should be above the water table, and if 

possible, the fill should be placed in a funnelshaped depression to prevent dispersal of the 

leachate. In such sites, most leachate in groundwater and surface-water flow can be suitably 

collected or contained in one or two ponds, 

and this water can be disposed of or treated as 

dictated by the chemical composition of the 

leachate. 

To summarize the above discussion, an acceptable landfill site in the Piedmont, ( 1) 

should be where the water table is at least 10 

feet (3 m) below land surface; (2) should not 

be adjacent to a stream or a large body of 

water, especially if the surface water is a 

source of public supply; (3) should not be 

where bedrock is within several feet (a few 

meters) of land surface, especially where the 

bedrock is highly creviced or fractured porous 

rock; and ( 4) should be near an adequate 

source of suitable cover material (overburden). 

Several reports can be used to evaluate landfill sites according to the above-mentioned hydrologic and geologic criteria. U.S.G.S. openfile report 76-881 (Richardson, 1976a) shows 

depth to water table in Montgomery County 

and can be used to eliminate areas where the 

water table is less than 10 feet (3 m) below 

the land surface. Such areas pose severe hazards for contamination of surface and (or) 

ground water because downward-percolating 

leachate may reach the water table without 

losing many of its undesirable constituents. 

Proposed sites can be further evaluated by consulting map I-920-B (Froelich, 1975h), which 

shows thickness of overburden in Montgomery 

County. Sites proposed in areas where over20 
FIGURE 11.- Completed sanitary landfill at Oxon Run, Prince Georges County. 

burden thickness is less than 20 feet (6 m) can 

be ranked lower than sites in areas having 

more overburden. Moderately well drained sites 

in interstream areas where the water table is 

more than 35 feet (10.6 m) below the land surface pose fewer hazards for waste disposal than 

sites where the water table is shallower than 35 

feet (10.6 m). 

Map I-920~D (Froelich, 1975a) is also useful as a guide in the selection of sanitary-landfill sites. For example, this map shows that the 

western part of Montgomery County is underlain by siltstone and sandstone (S1 and S2). 

Table 1 of map I- 920- D indicates that these 

units have a thin overburden and are highly 

jointed and fractured. Rocks of this nature 

may permit rapid movement of landfill leachate 

into the underlying ground water or into nearby streams. Hence, extreme caution is warranted in selecting sites in units S1 and S2. 

The selection of a landfill site in the Coastal 

Plain generally involves the same criteria discussed for Piedmont sites. However, detailed 

onsite knowledge of the subsurface geology 

and the direction and depth of ground-water 

movement is needed here also. In general, outcrop and shallow subcrop areas of major sand 

21 

aquifers should be avoided, especially if the 

aquifer is being recharged in the area of the 

landfill. Map MF-768-B (Hack, 1976a) and 

U.S.G.S. open-file report 76-197 (Richardson, 

1976d) can be used as preliminary guides to selecting acceptable landfill areas in Prince 

Georges County. However, most site evaluations will require detailed drilling to determine the nature of the deposits overlying major 

aquifers and to ascertain whether or not 

ground water is moving downward at the site. 

Of course, selection of landfill sites involves 

other considerations beyond those pertaining to 

geologic and hydrologic factors, but these other 

criteria are not discussed in this paper. Any 

final selection of a sanitary landfill site must be 

based on detailed engineering and geohydrologic studies of any proposed site by specialists 

qualified in this field. The map reports discussed in this Circular should be used only as 

preliminary guides and as sources of basic 

geologic and hydrologic information. 

COMPUTER MAPPING AND LAND-USE PLANNING 

The various field studies that were done as 

part of the Baltimore-Washington Urban Area 

Study resulted in a large amount of planning-
:mmm:m::mmm:mm:mm:mmmm:mmmmmHmmm::mm:mmmHHmmmmmmm::mmmm:mmmmmmmnmmm:mmm:mmn:m::m:::m:mmmm:mmmm:m m:mntm~m.m~~mmum:mlmmmm~mmmn~!lli! mmmmamwwmummmmmm:mmummmnmmu4!UU4umuuuuuJIIIJII IJII!!!!!.!U!!!~uuuuuwu~muwumlmlum} 

tm~!!!!!ltUmuu!l!m:lmll!!m:~~~~~~;::~mummml!!mmnm!r.m~mlti?lllllllll!mmu;u:mlwm:!illli:IU!l!!!l!l:UUmm;:l!l!lm:~:l!ii~uu~u•uttm:u~u!!::::u:il!!!llmmu!&m:. 

.. :! 

.:& 

t!H~H!·\:'H!i:t!l;:•:mtY!JI:·H lij:i::!ih'!~ii:H: ~il:'~! : 

::m~~5)Hii':i!:lr1£t!!1.=::n~.:;rm.:::~:m.11f!!FB:i;:n::;: ·· 

c ... ••>< ·~n h•~••,•·~ 

YUlUU (Un " , . .., ... ~,. '""00. " ·: .. !& .. ~ -~ .. !& lg~ .. ~ 

ouo ""'""~ uu•H<•s ... u.u <LHI • " , • .., ..... u F.-(100. " •• t~ 1 '! 1 '& .. 'l "' ·: 

-· ' !:fllllt'" ...... '"""' 

--·' ~'.l i! l!ll ~l !~!Il ~" 

··> , !:U~O • lfOo«• ' "" s.,.•ocr 

··) o OQOO .. OO. &U•IOU,.Olllf 

FIGURE 12.-Computer composite map showing some 

of the conditions affecting sanitary-landfill sites, 

Montgomery County. From 

Stewart and Van Driel 

(1975) 0 

CONDITIONS AFFECTING 

LANDFILL 

!IHilllmnn::mn:mnnuu:mnm:::~::m:mlmm:JnnmnmnmlnmmlnlniHmm:mmmmmmmm:m::mmmmmmmmmmnp:munm:mmw:~ uu:m:mmmmmmmmlmm 

mmmlllllllllllllli!lllllllUIIUillllW;iWilHHIIi!WillllWi!!miimm!!UHHHUI!!l!!!!li!!!!U!HIIlliiiiUIUIH!WIIIl!ii!UUUIUWIUUIIIllii/IIII!IIIIIIUWUWllllill!ll!lliUUUlUllllHH!I!HlUllll 

!l!l~lU!l!!il!I!Uillll8l!l:llllll~m:l!!!lJ111ii:<JU!!!!UilU!!II~l!~~UIInl!l:m!!ili!!l:liiU!UU:I!Illl!!!!ll:ll!~mllllllll!ll!l/lll IU!!l!UI!U!!IIp:111iiUIIU::IIiiii~IIWIUIIUl!IIH!I!!l!U:I!!!!I!!&I!I!l 

- ---------------------------------------------------------------------------------------------------------------------------------------------------------·--'----------------------------------------
MONTGOMERY COUNTY, 

MARYLAND 

,-.tc·'"~ -ti-r - i1·. L-"' - 1 

~ --r ;-.-.,.-.• :.:::. ' . ·-· ~ _;_; 

::mHmmm::m::::mmmm:m:m::m:mm:mmm :mm:::mm:m:m::Hmm:m::mmmm:m:mm::m;mmm:m:::uu:m:mm:mmuuu:uu::u:m:::u:mm:m::::::mu:mmu~::: 

:u::::JJI!llllllllli!MlM!UJ~om:m::mmmmnnmm:::muuum:::::::r:::::::~:~:~~im:::mm~!lmlmm~r.mr.!&!".!!!W.:!lllllm:::::::::mm:::::::m:::uu::::m: :I:J:lJIIIIll!llllllllllllllllllll\ 

uutuu;;m~mnmuulmnmm~&tm;:uumsunuul&uu:~m~u~u~~m~ui~m~?lm!~~~untu~u~~mittnm~uuuggt~~~~u~:t~&m;m&ld:nz:;m&u~?~~m&uuu~u~:u~m~uuutm~um~ttu;:uuu~ 
oriented earth-science information, most of 

which is presented in map reports. In order 

to derive the maximum benefit from these 

maps, a part of the project was designed to provide a computerized information system that 

would permit planners to combine already 

existing planning maps with the new geologic 

information. These data were combined by use 

of a cell-based computer-composite-mapping 

program which stores map information and enables the planners to retrieve information from 

single maps or combinations of maps at any 

scale for a particular geographic area. Montgomery County, Md., was divided into 4.5-acre 

(1.8-hectare) cells by using a latitude-longitude reference system, and county maps showing: (1) contours on base of saprolite, (2) bedrock type, (3) surface materials, ( 4) topography, (5) drainage network, and (6) land 

cover and vegetation were digitized. 

Information from the surface-materials and 

drainage-network maps was combined by the 

computer to produce a composite map showing 

some of the conditions affecting sanitary-landfill siting in the county (fig. 12). Figure 12 

shows all the areas within the county that have 

the combination of physical characteristics 

considered optimum for a sanitary-landfill site, 

as well as those areas having one or more undesirable features. As no ground-water data 

were then available, this aspect of the siting 

limitations was not considered. 

The digitized earth-science maps and computer system were installed in the MNCPPC 

computer in June 1976 and are presently being 

used by urban and environmental planners to 

create and revise master plans for Montgomery 

County. 

REFERENCES CITED 

[Map reports preceded by an asterisk were prepared as part of the Baltimore-Washington Urban Are:t Study] 

Cleaves, E. T., 1964, Mineral resources of Montgomery 

and Howard Counties, in The geology of Howard 

and Montgomery Counti·es: Baltimore, Maryland 

Geol. Survey, p. 262-269. 

*Cleave,s, E. T., Crowley, W. P., and Kuff, K. R., 1974, 

Towson quadrangle: Maryland Geol. Survey Geol. 

and Environmental Atlas, scale 1:24,000. (Include's 

maps showing geology, landforms, estimated thickness of ov;e,rburden, geologic factors affecting land 

modification, and mineral-resources and mined-land 

inventory.) 

Cloos, Ernst, and Cooke, C. W., 1953, Geologic map of 

Montgomery County [Maryland] and the District 

of Columbia: Baltimore, Md., Maryland Dept. Geology, Mines and Water Resources, scale 1:62,500. 

Cooke, C. W., and Cloos, Ernst, 1951, Geologic map of 

Prince Ge,orges County [Maryland] and the District of Columbia: Baltimore, Md., Maryland Dept. 

Geology, Mines and Water Re,sources, scale 

1:62,500. 

Crooks, J. "\V., O'Bryan, Deric, and others, 1967, Water 

re,sources of the Patuxent River basin, Maryland: 

U.S. Geol. Survey Hydro!. Inv. Atlas HA-244, scale 

1:250,000. 

*Crowley, W. P., Reinhardt, Juergen, and Cleaves 

E. T., 1976, Geologic map of Baltimore County and 

City, map in pocket of Crowley, W. P., The geology 

of the crystalline rocks near Baltimore and its 

bearing on the evolution of the eastern Maryland 

Piedmont: Maryland Geol. Survey Rept. Inv. 27, 40 

p., scale 1:62,500. 

Darton, N. H., 1947, Sedimentary formations of Washington, D.C., and vicinity: Washington, D.C., U.S. 

Geol. Survey, scale 1:31,680. 

Dingman, R. J., and Ferguson, H. F., 1956, The 

ground-water re,sources of the Piedmont part, in 

The wat,er resourees of Baltimore and Harford 

Counties: Maryland Dept. Geology, Mines and 

Water Resources Bull.17, p.1-128. 

Dingman, R. J., and Meyer, Gerald, 1954, The groundwater resources, in The water resources of Howard 

and Montgomery Counties: Maryland Dept. Geology, 

Mines and Water Resources Bull. 14, p. 1-139. 

Edwards, Jonathan, Jr., 1969, Mineral commodities 

of Maryland, in Ground-water aquifers and mineral 

commodities of Maryland: Maryland Sta.te Planning Dept. Pub. 152, p. 15-36. 

Fisher, G. W., 1964, The Triassic rocks of Montgomery 

County, in The geology of Howard and Montgomery 

Counties: Baltimore, Maryland Geol. Survey, p. 10-

17. 

--- 1970, The Piedmont; the metamorphosed sedimentary rocks along the Potomac River near Washington, D.C., in Fisher, G. W., Pettijohn, F. J., Reed, 

J. C., Jr., and Weaver, K. N., eds., Studies of Appalachian geology-central and southern: New 

York, InteTS·cienoe Publishers, p. 299-315. 

*Froelich, A. J., 1974, Natural soil assemblages map of 

Montgomery County, Maryland: U.S. Geol. Survey 

open-file rept. 74-70, 6 p., 1 pl., scale 1:62,500. 

*--- 1975a, Bedrock map of Montgomery County, 

Maryland: U.S. Geol. Survey Misc. Inv. Map I920-D, scale 1:62,500. 

*--- 1975b, Contour map of the base of saprolite, 

Montgomery County, Maryland: U.S. Geol. Survey 

Misc. Inv. Map I-920-C, scale 1:62,500. 

24 

*--- 1975c, Map showing contours on the base of 

saprolite, District of Columbia.: U.S. Geol. Survey 

open-file rept. 75-539, 3 p .. , 1 pl., scal·e' 1:24,000. 

*--- 1975d, Map showing mineral resources of 

Montgomery County, Maryland: U.S. Geol. Survey 

Misc. Inv. Map I-920-E, scale 1:62,500. 

*--- 1975e, Map sho·wing surface materials, Di,strict 

of Columbia: U.S. Geol. Survey open-file rept. 75-

540, 2 p., 2 pis., scale 1:24,000. 
*--- 1975f, Map showing thickness of overburden, 

District of Columbia: U.S. Geol. Survey open-me 

rept. 75-538, 4 p., 1 pl., scale 1:24,000. 

*--- 1975g, Surface materials map of Montgomery 

County, Maryland: U.S. Geol. Survey Misc. Inv. 

Map I-920-A, scale 1:62,500. 

*--- 1975h, Thickness of overburden map of Montgomery County, Maryland: U.S. Geol. Survey Misc. 

Inv. Map I-920-B, scale 1: 62,500. 

*Froelich, A. J., and Hack, J. T., 1975, Preliminary 

geologic map, District of Columbia: U.S. Geol. Survey open-file rept. 75-537, 8 p., 1 pl., scale 1:24,000. 

Geological Society of America, Committee on Environment and Public Policy, 1975, Geologic constraints 

in the urban environment: Boulder, Colo., 12 p. 

Glaser, J. D., 1971, Geology and mineral resources 

of southern Maryland: Maryland Geol. Survey Rept. 

Inv. 15, 84 p., geol. map, scale 1:200,000. 

*--- 1973, Bowie quadrangle: Maryland Geol. Survey Geol. and Environmental Atlas, 3 p., scale 

1:24,000. (Includes maps showing geology, mineral 

resources, general construction conditions, constraints on septic tanks, and ground-water resources.) 

Hack, J. T., 1955, Geology of the Brandywine area 

and origin of the upland of southern Maryland: U.S. 

Geol. Survey Prof. Paper 267-A, 43 p. 

*--- 1976a, Map of construction conditions, Prince 

Georges County, Maryland: U.S. Geol. Survey Misc. 

Field Studies Map MF-768-B, scale 1:62,500. 

*--- 1976b, Map of mineral resources, Prince 

Georges County, Maryland: U.S. Geol. Survey Misc. 

Field Studies Map MF-768-A, scale 1:62,500. 

*--- 1977, Geologic map for land-use planning, 

Prince Georges County, Maryland: U.S. Geol. Survey Misc. Inv. Map I-1004, scale 1:62,500. 

Hansen, H. J., III, 1968, Geophysical log cross-section network of the Cretaceous sediments of southern Maryland: Maryland Geol. Survey Rept. Inv. 

7, 46 p., 8 figs., 17 pis. 

*Herb, W. J., 1976a, Availability of hydrologic data for 

Montgomery County, Maryland: U.S. Geol. Survey 

open-file rept. 76-884, 15 p., 1 pl., scale 1:62,500. 

*--- 1976b, Availability of hydrologic data for 

Prince Georges County, Maryland: U.S. Geol. Survey open-file rept. 76-178, 7 p., 1 fig., scale 1:62,500. 

Higgins, M. W., and Fisher, G. W., 1971, A further 

revision of the stratigraphic nomenclatu~e of the 

Wissahickon Formation in Maryland: Geol. Soc. 

America Bull., v. 82, no. 3, p. 769-774. 

Hopson, C. A., 1964, The crystalline rocks of Howard 

and Montgomery Counties, in The geology of Howard and Montgomery Counties: Baltimore, Maryland 

Geol. Survey, p. 27-259. 

Imhoff, E. A., Kocke:lman, W. J., O'Connor, J. T., and 

LaFevers, J. R., 1978, Methods and criteria for land 

use and resourc·es planning in surface mined areas, 

Vol. 2 of Int,egrated mined-area reclamation and 

land-use planning: Argonne Natl. Lab., ANL/EMR1, 56 p. 

Jacobeen, F. H., Jr., 1972, Seismic evidence for high 

angle :veverse faulting in the Coastal Plain of 

Prince Georges and Charles County [sic], Maryland: Maryland Geol. Survey Inf. Circ. 13, 21 p., 

10 figs., 2 pis. 

Johnston, P. M., 1964, Geology and ground-water resources of Washington, D.C., and vicinity: U.S. 

Geol. Survey Water-Supply Pap·er 1776, 97 p. 

--- [18·66?], Geology and ground-water resources 

of Washington, D.C., and vicinity [Unpublished appendix of well logs and drill-hole data for U.S. 

Geol. Survey Water-Supply Paper 1776] : Washington, D.C., n.p. [Available in U.S. Geol. Survey Library, Reston, Va.] 

Kirby, R. M., Matthews, E. D., and Bailey, M. A., 

1967, Soil survey of Princ.e Georges County, Maryland: Washington, D.C., U.S. Soil Conserv. Service, 

170 p. 

Knechtel, M. M., Hamlin, H. P., Hosterman, J. W., 

and Carro.Jl, Dorothy, 1961, Physical properties of 

nonmarine Cretaceous clays in the Maryland 

Coastal Plain: Maryland Dept. Geology, Mines and 

Water Re:sources Bull. 23, 11 p. 

*Kuff, K. R., 1975, Mined land inventory map of Baltimore County and Baltimore City: Baltimore, Maryland Geol. Survrey, scale 1: 62,500. 

25 

Larrabee, D. M., 1969, Serpentinite and rodingite in 

the Hunting Hill quarry, Montgomery County, 

Maryland: U.S. Geol. Survey Bull. 1283, 34 p. 

Leopold, L. B., 1968, Hydrology for urban land planning-A guidebook on the hydrologic effects of 

urban land use: U.S. Geol. Survey Circ. 554, 18 p. 

Leopold, L. B., Clarke, F. E., Hanshaw, B. B., and 

Balsley, J. R., 1971, A procedure for evaluating environmental impact: U.S. Geol. Survey Circ. 645, 

13 p., 1 pl. 

Mack, F. K., 1966, Ground water in Prince Georges 

County: Maryland Geol. Survey Bull. 29, 101 p. 

Maryland-National Capital Park and Planning Commission, 1968-1972, Land-us1e maps of Montgomery 

County, Maryland: Silver Spring, Md., scale 

1:12,000. 

--- [1977], Slope map of Montgomery County, 

Maryland: Silver Spring, Md., scale 1:62,500. 

Matthews, E. D., Compy, E. Z. W., and Johnson, J. C., 

1961, Soil survey of Montgomery County, Maryland: U.S. Soil Conserv. Service, Soil Survey Series 

1958, no. 7, 107 p. 

*Mayer, Larry, 1977, Drainage basin map of Montgomery County, Maryland: U.S. Geol. Survey openfile rept. 77-512, 3 p., 1 pl., scale 1:62,500. 

Meyer, Gerald, 1952, Ground-water resources of 

Prince Geo·rge,s County, in Geology and water resources of Prince Georges. County: Maryland Dept. 

Geology, Mines and Water Resourc.es Bull. 10, p. 

82-257. 

Nutter, L. J., 1974, Well yields in the bedrock aquifers 

of Maryland: Maryland Geol. Survey Inf. Circ. 16'-1 

24 p. 

--- 1975, Hydrogeology of the Triassic rocks of 

Maryland: Maryland Geol. Survey Rept. Inv. 26, 

37 p. 

Nutter, L. J., and Otton, E. G., 1969, Ground-wa,ter 

occurrence in the Maryland Pi·edmont: Maryland 

Geol. Survey Rept. Inv. 10, 56 p. 
Otton, E. G., 1955, Ground-water resources of the 

southern Maryland Coastal Plain: Maryland Dept. 

Geology, Mines and Water Resource's Bull. 15, 347 

p., 26 figs., 15 pis. 

*Otton, E. G., Cleaves, E. T., Crowley, W. P., Kuff, 

K. R., and Reinhardt, Juergen, 1975, Cockeysville 

quadrangle; Geology, hydrology and mineral resourc,es: Maryland Geol. Survey Quad. Atlas 3, 4 

p., scale 1:24,000. (Includes maps showing geology, 

estimated thickness of overburden, geologic factors 

affecting land modification, mineral-resources and 

mined-land inventory, location of wells, springs, and 

test holes, depth to the water table, availability of 

ground water, geohydrologic C'onditions pertaining 

to domestic underground liquid-waste disposal.) 

*--- 1978, White Marsh quadrangle; Geology, 

hydrology and mineral resources: Baltimore, Maryland Geol. Survey (Includes maps showing g·eology, 

physiography, estimated thickness o.f overburden 

mineral-resources and mined-land inventory, loca~ tion of wells and springs, depth to the wat1er table, 

availability of ground water, and geohydrologic 

conditions pertaining to domestic liquid-waste disposal.) 

Papadopulos, S. S., Bennett, R. R., Mack, F. K., and 

Treseott, P. C., 1974, Water from the Coastal Plain 

aquifers in the Washington, D.C., metropolitan al'lea: 

U.S. Geol. Survey Circ. 697, 11 p. 

Pearre, N. C., compiler, 1961, Mineral deposits of 

Maryland, excluding fuels, sand, and gravel: U.S. 

Geol. Survey Mineral Inv. Resources Map MF -12, 

scale 1:250,000. 

Reed, J. C., Jr., and Jolly, Janice, 1963, Crystalline 

rocks of the Potomac- River Gorge near Washington, 

D.C.: U.S. Geol. Survey Prof. Paper 414-H, 16 p. 

Reed, J. C., Jr., and Reed, J. C., 1969, Gold veins near 

Gveat Falls, Maryland: U.S. Geol. Survey Bull. 

1286, 22 p. 

*Richardson, C. A., 1976a, Approximate depth to the 

water table, Montgomery County, Maryland: U.S. 

Geol. Survey open-file rept. 76-881, 4 p., 1 pl., scale 

1:62,500. 

*--- 1976b, Ar,eas of shallow wa,ter table, Prince 

Georges County, Maryland: U.S. Geol. Survey openfile rept. 76-194, 3 p., 1 fig., scale 1:62,500. 

*--- 1976c, Availability of ground water in Montgomery County, Maryland: U.S. Geol. Survey op.enfile rept. 76-882,13 p., 1 pl., scale 1:62,500. 

*--- 1976d, Availability of ground water in Prince 

Georges County, Maryland: U.S. Geol. Survey openfile rept. 76-197, 9 p., 4 figs., scale 1:62,500. 

Robinson, G. D., and Spieker, A. M., eds., 1978, Nature 

to be commanded * * *: U.S. Geol. Survey Prof. 

Pap·er 950, 95 p. 

*Roen, J. B., and Fro,elich, A. J., 1976, Contour map 

of the base o.f saprolite, Howard County, Maryland: 

U.S. Geol. Survey Misc. Field Studies Map MF772-A, scale 1: 62,500. 

*--- 1978, Thickness of overburden map, Howard 

County, Maryland: U.S. Geol. Survey Misc. Field 

S.tudi,es Map MF-772-B, scale 1:62,500. 

26 

Southeastern Wis·consin Regional Planning Commission, 1968, Floodland and shoreland development 

guide: Waukesha, Wis., Southeastern Wisconsin 

Regional Planning Comm. Planning Guide 5, 199 p. 

*Stewart, J. C., and Van Driel, J. N., 1975, The application of a computerized ~environmental information system to master and sector planning: Maryland-Nat!. Capital Park and Planning Comm. Environmental Planning Mon. 8, 34 p. 

U.S. Geological Survey, 1967a, Engineering geology of 

the Northeast Corridor, Washington, D.C., to 

Boston, Massachusetts-Bedrock geology: U.S. Geol. 

Survey Misc. Geol. Inv. Map I-514-A, 9 p., 7 sheets, 

scale 1:250,000. 

--- 1967b, Engineering geology of the Northeast 

Corridor, Washington, D.C., to Boston, Ma,ssachusetts-Coastal Plain and surficial d.eposits: U.S. 

Geol. Survey Misc. Geol. Inv. Map I-514-B, 9 p., 

sheets 1-5, scale 1:250,000; sheet 8, scale 1:1,500,000. 

U.S. Soil Conservation Service, Engineering Division, 

1975, Urban hydrology for small wa,tersheds: U.S. 

Soil Conserv. Service Tech. Release 55, variously 

paged. 

*Van Driel, J. N., 1975a, Digital computer map showing conformation of the bedrock surface, Montgomery County, Maryland: U.S. Geol. Survey openfile rept. 75-418, 1 pl., scale 1:48,000. 

*--- 1975b, Digital computer map showing surface 

materials, Montgomery County, Maryland: U.S. 

Geol. Survey open-file rept. 75-419, 1 pl., scale 

1:48,000. 

*--- 1975c, Digital topographic map of Montgomery 

County, Maryland: U.S. Geol. Survey open-file rept. 

75-420, 1 pl., scale 1:48,000. 

*--- 1975d, Map showing conditions affecting sanitary landfill siting in Montgomery County, Maryland: U.S. Geol. Survey open-file rept. 75-177, 1 pl., 

scale 1:48,000. (A computer c·omposite map.) 

*Van Driel, J. N., and Stewart, J. C., 1976, The role 

of computer mapping in the decision-making process 

for Montgomery County, Maryland: Review of Public Data Use, v. 4, no. 4, p. 31-40. 

Waananen, A. 0., Limerinos, J. T., Kockelman, W. J., 

Spangle, W. E., and Blair, M. L., 1977, Flood-prone 

areas and land-use planning-selected examples 

from the San Francisco Bay region, California: U.S. 

Geol. Survey Prof. Pap·er 942, 75 p. 

William Spangle and Associates, F. B. Leighton and 

Associates, and Baxter, McDonald and Company, 

1976, Earth-science information in land-use planning-Guidelines for earth scientists and planners: 

U.S. Geol. Surv'ey Circ. 721, 28 p. 

':'Withington, C. F., and Froelich, A. J., 1974a, Preliminary geologic ma.p of the Beltsville quadrangle, 

Prince Georges, Montgomery, and Howard Counties, 

Maryland: U.S. Ge·ol. Survey Misc. Field Studies 

Map MF-582, 2 sheets, scale 1:24,000. 

*--- 1974b, Selected geologic data for the Beltsville 

quadrangle, Prince Georges, Montgomery, and 

Howard Counties, Maryland: U.S. Geol. Survey 

open-file rept., 10 p., 1 fig., 1 pl., scale 1:24,000. 

-k U.S. GOVERNMENT PRINTING OFFICE: 1980 0- 311-344'71