Nature

to e

^^

Commanded

Earth-science maps applied to

land and water management

GEOLOGICAL SURVEY PR
Tualatin Valley near Portland, Oregon

All over the country, orchards, farms, and undeveloped lands near cities are 

being rapidly turned into freeways, industrial parks, shopping centers, and 

housing projects. Use of earth-science maps can help insure that the coming 

developments make the fullest use of natural resources and are exposed to 

the minimum risk from natural hazards. (Photograph by Oregon Highway 

Department)

Cover: An artist's rendition of the concept evoked by the photograph above. The city reaches out to take over the 

countryside. The process has not gone very far, symbolizing the idea that the earth sciences can make their best 

contribution at an early stage. The geologic detail revealed at the bottom is a reminder that the rocks and waters 

beneath the surface are critically important to intelligent land and water management.

UNITED STATES DEPARTMENT OF THE INTERIOR Cecil D. Andrus, Secretary

GEOLOGICAL SURVEY W. A. Radlinski, Acting Director
"Nature

to be

Nature to be commanded 

must be obeyed"

Francis Bacon, "Novum Organum," 1620

Commanded ...

Earth-science maps applied

to land and water management

GEOLOGICAL SURVEY PROFESSIONAL PAPER 950

G. D. Robinson and Andrew M. Spieker, editors

Demonstrates the value of earth-science information in land and water

management by showing how earth-science maps have been used

in making plans and decisions in a variety of urban settings

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON

1978
Foreword

Anyone familiar with Professional Papers of the Geological Survey 

will find this one very different. Professional Paper 950 is different 

not only in appearance but also in style and content, because it is 

designed for a different audience: namely, anyone interested in the 

well-being of cities, and especially those involved in urban planning, 

design, management, and development. Its publication signals an 

expanding commitment by the Survey to study and understand the 

earth-science aspects of the urban environment.

This activity is a natural consequence of history. When the Survey 

was founded in 1879, the population of the United States was about 

50 million, of whom three-fourths were farmers. Today the population exceeds 215 million, of whom three-fourths are city dwellers. 

The early Survey concentrated on providing earth-science services 

to aid agriculture and to find and develop the resources of the 

hinterland; the Survey today must increasingly provide earth-science 

services to help make our cities safer, healthier, and happier.

One problem the Survey faces in trying to discharge its growing 

urban responsibility is that most of its potential urban users are 

unaware of what earth science has to offer. With this book we hope 

to help solve the problem by demonstrating with actual examples 

some of the many ways that earth-science information can be effectively applied to urban planning and decisionmaking.

Much of the essential earth-science information for urban 

environments is not yet available. However, increasing awareness 

of the need for an application of such information can accelerate 

its development by both private and public agencies.

William A. Radlinski 

Acting Director

First printing 1978 

Second printing 1979

Library of Congress Cataloging in Publication Data

"Nature to be commanded..." Geological Survey Professional Paper 950 Bibliography: p. 93-95 

1. Land use-Planning-United States-Case studies. 2. Earth sciences-United States-Maps 

I. Robinson, GershonDu Vail, 1918- II. Spieker, Andrew Maute, 1932-

III. Series: United States Geological Survey Professional Paper 950 

HD 205 1977.N37 333.7'0973 77-608265
ontents

1

21

30

42

47

52

55

90

INTRODUCTION G. D Robinson and Andrew M. Spi

APPLICATIONS IN A PACIFIC COAST ENVIRONMENT 

Central San Mateo County, California

* Land-use controls arising from erosion of s< a cliffs, 

landsliding, and fault movement Briari^AUvater

APPLICATIONS IN AN ARID ENVIRONME 

Tucson, Arizona

conserving mineral and water resources 

F. S. Davidson, J. H. FetK

,ft

M. Spieker

APPLICATIONS IN A MOUNTAIN FRONT ENVIRONMEN 

Front Range Urban Corridor, Colorado

In the Boulder are.i:

* Guiding development of gravel deposits and of unstable ground 

E. J. Crosby, W. R. Hansen. and J. A. Pendleton

In the Colorado Springs area:

# Water for new communities in El Paso County 

R. K. Litingston and T M. Sundaram

______________________ \

APPLICATIONS IN A NEW ENGLAND ENVIRONMENT 

Connecticut River valley, Connecticut

* East Granby: A plan oJt development for a rural community 

William H. I.*ngei and Lawrence H. Johnson

jMJse of drainage-area maps in evaluating waste-disposal conditions, 

assessing the impact of highway salting, and designing 

bridges and culverts Robert L. Melvii

APPLICATIONS IN AN ATLANTIC COAST ENVIRON 

Nassau County, Long Island, New York

# Water management in humid country B. L. Foxworthy

APPLICATIONS IN AN ATLANTIC COAST ENVIRONMENT

Franconia area, Fairfax County. Virginia m**- **

# Planning a new community in an urban setting: Lehigh

A. J. Froelich, A. D. G.upaas. and J. N. Van Driel

CLOSING THOUGHTS G. D. Robinson and Andrew M Spieker

91 SOURCES

1

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isr

 vT

Ill

^ E A R T H Q VU A^K E^

s

'X

action

 1.

By G. D. Robinson and Andrew M. S]

LAVA FLOW

B 99?-

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I til

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filature's forces and processes continue 

virtually unimpeded by even the largest 

works of man. Moreover, when man builds 

and lives in concert with nature, his works 

may persist for generations; when he does 

not, the products of his labors, and sometimes man himself, are soon obliterated. 

As Francis Bacon observed, "Nature to be 

commanded must be obeyed!" To be 

obeyed, nature must be understood.

The earth sciences have developed many 

tools for observing nature's forces and 

processes and for documenting the changes 

in our environment that result from them. 

These tools help to understand nature 

better, including the opportunities presented by resources and the deterrents 

posed by hazards. If used properly, these 

tools can help us live in concert with nature. 

Some of the most valuable tools and the 

most readily understood are earth-science 

maps.

« *<*

&*?

FLOOD
Why earth-science 

maps

Earth-science maps portray the Earth's surface; the 

rocks, unconsolidated materials, and waters on and 

beneath the surface; and the processes that make and 

change them. This book shows how such maps have 

been used in making plans and decisions in a variety 

of urban and suburban settings. Its purpose is to 

demonstrate, by examples from across the country, 

that the use of earth-science information in map form 

can lead to large returns in both public and private 

benefits, measurable nearly always in dollars and 

usually in social and cultural values.

In a very real sense, the book is a form of 

institutional advertising. The "institution" being 

advertised is earth science, or, as it used to be called, 

geology. For its value to mineral, water, and energy 

development, earth science needs no advertising. 

When copper or oil is being looked for or developed, 

geologists and geophysicists are customarily consulted; when a city needs more water, hydrologists 

and hydraulic engineers are regularly brought in. But 

earth science has not been, and is not being, used to 

anything like its full potential in the planning, 

development, and management of urban and urbanizing areas.

Neglect of earth science

Evidence of this neglect abounds. It is most obvious 

in the urban damage wrought by catastrophic 

geological hazards floods and earthquakes; less 

spectacular but far more costly, in terms of property if 

not lives, is damage due to such geological hazards as 

coastal erosion, landslides, expansive soil, and 

subsidence by compaction or into caves and mines. 

Annual losses from geological hazards are estimated 

in the table above; except for floods, these losses, 

aggregating billions of dollars, are concentrated in 

urban areas. The figures cited, coming from varied 

sources using different assumptions, are crude and 

hard to compare, but their import is plain: The price 

of ignoring nature is high.

What can be done about losses from these acts of 

nature? Nothing, of course, about those that have 

already happened, but much can be done to stop or 

reduce losses from events yet to come. Armed with 

information that indicates the kind, degree, and 

location of potential hazards, planners and decisionmakers can forestall or relocate new developments in 

areas where lives and property would be imperilled, 

they can propose appropriate design precautions in 

developments that cannot be placed elsewhere, and 

they can alert inhabitants of imperilled developments 

to seek protection through engineering or insurance.

Mean annual 

losses in the 

United States 

from geological hazards

HAZARD

LIVES 

DOLLARS

FLOODS

EARTHQUAKES

LANDSLIDES

COASTAL EROSION

EXPANSIVE SOIL

OTHERS

$1 200 MILLION

51 000 MILLION

$300 MILLION

Unknown

p 

L

MILLION |

Unknown

$100 MILLION

Others: subsidence, creep, fault displacement, liquefaction of sand 

and clay, dust, waves caused by earthquakes, volcanoes

For sources, see page 93.

Houses that are not built on f loodplains or f loodways 

will not be damaged or swept away by floods; 

buildings in high-risk earthquake areas that do not 

have unsecured facades will not shower those ornaments on passersby when the earthquake comes; 

structures that are not built on unstable ground will 

not be damaged by sinking, swelling, or sliding.

Neglect of earth-science information is evident also 

in the mounting losses of mineral, water, and agricultural resources due to inadequately controlled 

urbanization: When sand and gravel or coal deposits, 

ground-water recharge areas, or prime agricultural 

lands are built over, the inevitable result is rising cost 

of basic construction materials, of fuel, of potable 

water, of food. National estimates for these costs have 

not been made, but are surely in the billions of dollars 

annually. For example, estimates made for California 

indicate that the annual loss due to building-over 

construction materials alone, or otherwise rendering 

them inaccessible, is greater than $500 million. 1 And 

the social costs, in diminished well-being, health, and 

safety are incalculably high. Little can be done about 

loss of resources that has already occurred, but with 

the aid of maps that show the developed and 

potential resources of an area, planners and decisionmakers can evaluate the costs of foregone resources 

due to proposed developments, and respond 

appropriately.

Finally, failure to use earth-science information is 

apparent in the rapid growth of man-made and manaided geological hazards: Collapse of slopes due to 

excavation for structures or roads; subsidence of land 

due to mining or to the withdrawal of water or gas or 

oil; contamination of ground water and surface water 

due to improper waste disposal.

\ Moderate damage 

r Major damage

Damaging earthquakes 

in the United States

This record indicates 

that 70 million Americans 

live with a significant 

earthquake risk, and another 115 million are exposed to a lesser, but not 

negligible, risk

Geological hazards and wasted or withdrawn 

natural resources are not restricted to a few unlucky 

places but occur throughout the country. Floods, 

water shortages, and conversion of good farmland to 

other uses (2 million acres per year) occur in all parts 

of the Nation; it is not so widely realized that 

earthquakes, landslides, and expansive soil are 

national problems too, as the maps on these pages 

testify. Few cities have reached satisfactory long-term 

solutions to waste disposal, which usually involves 

selecting suitable geologic and hydrologic settings. 

Yet only a handful of communities are using earthscience information systematically in reaching land 

and water management decisions.

(From National Oceanic and Atmospheric Administration, 1970)

Symbols locate epicenters only; 

areas affected were much larger

' 'References are omitted throughout the text but are listed, by chapter, on pages 

93-95.

Overcoming this neglect

The widespread failure to use earth-science 

information results mainly from lack of awareness of 

what the earth sciences have to offer. For its part, the 

earth-science profession is just beginning to develop 

its usefulness in the urban sphere. This book 

publicizes that usefulness. It is addressed to everyone 

interested in the health, safety, and prosperity of 

urban areas and specifically to the "planning 

community," those who directly influence land-use 

decisions in urban areas, such as planners, architects, 

engineers, government officials, legislators, judges, 

developers, and officers of financial institutions. (In 

trying to reach so broad an audience we have 

simplified and condensed our material to the point 

where many professional planners, engineers, and 

architects may find it too elementary.)

Earth scientists can help the urban planner and 

decisionmaker by providing information on the 

resources to be developed, conserved, or protected 

until needed and on the hazards to be avoided or 

mitigated. To do so in words, tables, or numbers 

rarely suffices, for the user needs to know not only 

WHAT, HOW, HOW MUCH, and WHEN, but also 

WHERE. Telling WHERE requires maps. Information 

on maps can also help to answer the other questions. 

Few earth-science maps, however, are made specifically for working with urban problems, and therefore 

few can be put to urban use exactly as they come from 

the mapmaker. Topographic maps and slope maps 

can be used directly for preliminary planning of such 

engineering works as highways, pipelines, powerlines, airports, and drainage facilities, and for 

planning housing location and density. But most 

geologic and hydrologic maps must be translated 

from technical to operational or practical terms and 

interpreted in various ways for various uses. For many 

uses, information must be brought together from 

several maps, requiring synthesis as well as translation 

and interpretation; often, map data must be supple-
Swelling clay in nearsurface rocks in the 

United States

Swe///ng clay (montmorillonite) is the main cause 

of expansive soil

I | Regionally abundant 

| | Locally abundant

Minor constituent of bedrock 

but may be locally abundant 

in surf icial materials

(From Tourtelot, 1974)

mented by data from laboratory or field tests. Earthscience maps and related data can thus be used to 

generate many kinds of derivative or interpretive 

maps valuable to the planning community, such as 

ease of excavation, landslide susceptibility, slope 

stability, seismic susceptibility, capability for solid 

waste disposal, percolation rates, subsidence potential, mineral potential, availability of construction 

materials, recreation potential, and scores more.

The number of earth-science maps needed depends on the use. Sometimes, as noted above, a single 

map will suffice. To determine the rate of seacliff erosion as a basis for regulating building setbacks, three 

maps are needed: one of the height of the seacliffs, 

one of their slope, and one of the kind of underlying 

rock or unconsolidated material. For an extreme 

example, planning a new town may require 15 to 20 or 

more earth-science maps. Earth-science maps, therefore, may be needed singly, in squads, or in platoons.

Scope of this book

This book seeks to illustrate and illuminate the 

preceding discussion by samples of practical applications from six areas: central San Mateo County, 

California; Tucson, Arizona; the Front Range Urban 

Corridor, Colorado; the Connecticut River Valley, 

Connecticut; Nassau County, Long Island, New York; 

and Fairfax County, Virginia. In these six areas a 

variety of climatic, geographic, geologic, hydrologic 

and cultural settings are represented: coastal and 

inland, mountains and plains, wet and dry, town and 

city, soft sediment and hard rock. But this book still 

provides only a meager sample of both applications 

and settings. To cover all known or potential 

applications, in every part of the country, would 

result in a thick and costly encyclopedia.

The samples chosen all result from recent or 

current work of the U.S. Geological Survey; no new 

mapping was done for this volume, and no use has 

been made of the excellent work that has been and is 

being done elsewhere by other Federal agencies, for 

example the Soil Conservation Service; by State 

geological surveys; by academic institutions; by some 

regional and local planning agencies; and by private 

consultants. A few of the samples in this book 

illustrate planning applications. But plans are not 

actions, and all too many plans never result in actions. 

Consequently, most of the samples chosen are 

examples of earth-science information that has 

contributed to actions in the form of regulations, 

ordinances, rulings, or laws by local, county, or 

State jurisdictions. A few examples are hypothetical, 

but they too are based on real cases.

For earth-science maps to be useful, they must be 

both relevant and understandable to potential users. 

These users are generally planners, whether professionally trained or not, for no matter who makes the 

final decision, planning is likely to be involved in the 

process. Therefore, professional planners have participated throughout the preparation of this book. 

Two chapters are coauthored by planners, and other 

planners reviewed the entire manuscript.

Though earth-science information is basic to the 

selected examples, the plans or decisions made were 

heavily influenced by social, economic, cultural, and 

political factors; consideration of these is omitted 

here. The treatment consists of describing a problem 

or situation, presenting the principal earth-science 

maps that bear on it, and then citing, either by 

quotation or paraphrase, the plan or decision that 

resulted. The Geological Survey's earth-scientists did 

not propose or advocate any particular course. Nor 

does citing the plans or decisions here imply 

judgment, favorable or unfavorable, by the earthscientist authors or by the Geological Survey.

Landslides and 

landslide potential 

in the United States

| | ABUNDANT - High future risk 

I | COMMON - Moderate future risk

I | FEW May slide if slopes disturbed by con 

struct/on or unusual precipitation

FEW - Low future risk

Earth-science maps pay

What we do advocate is that land-use plans and 

decisions be made with the fullest possible knowledge of the natural materials and processes that are 

involved. As Peter Flawn, former State Geologist of 

Texas, wrote recently, "Land-use planning that does 

not consider geologic data has diminished chances of 

success because not all of the pertinent data have 

been analyzed." Or, to repeat Francis Bacon's somewhat more poetic statement made 350 years ago: 

"Nature to be commanded must be obeyed."

This book is not a manual or a handbook or a 

textbook. It barely begins to tell how or when to use 

earth-science maps. There are already several such 

works, some of them available for years, but they 

seem to have had little impact on the world of urban 

action. (Some are cited in the reference list.) They 

have no doubt been used by earth scientists, but not 

often by those who plan or make decisions.

As all successful evangelists know, before you can 

save sinners, you must get them into the revival tent. 

That is what we hope to do: to place this book in the 

hands of a large proportion of the urban planning and 

decision-making community and inform those who 

have not yet received the message that earth-science 

information in map form, applied early and consistently, has been of economic benefit, has aided 

conservation and human values in many communities, and can probably do as much for theirs.

About earth-science 

maps

Earth-science maps exist in an abundance of kinds 

and scales, for earth science involves the forms, 

materials, and active processes of the whole Earth. 

The materials of the earth have almost innumerable 

properties, bear almost innumerable relationships 

to each other, and are acted upon by myriad forces 

and processes most of these can be portrayed in 

map form, and hundreds have been. Covering anywhere from a city lot to the entire planet, the scales 

of earth-science maps may range from very large, 

in which 1 inch on the map may represent a few feet, 

to very small, in which 1 inch may represent hundreds of miles. Only a small fraction of earth-science 

maps, however, is directly useful for urban application. In this book, we offer a modest sample of that 

fraction, beginning with a general look at some 

basic earth-science maps.

To use earth-science information 

effectively, it is necessary to have the 

help of earth scientists. To help find 

them we have listed on pages 91 92 

some offices of the U.S. Geological 

Survey and of State geological surveys 

or their equivalents. Most colleges and 

all universities have earth-science 

departments, and earth scientists are 

listed in the yellow pages of the telephone directory under such headings as 

Geologists, Engineers-Civil, EngineersConsulting, Engineers-Foundation, Hydrologists, Geophysicists (but not, as 

yet, Earth Scientists).

Sreatly simplified from National Overview Map 

by Radbruch-Hall and others. 1976)
^/A~X

Topograph maps

Their nature and 

urban uses

81

Maps that accurately show the shape of the land, 

the network of water features, and the positions and 

elevations of the works of man are essential to urban 

planning and management. Standard U.S. Geological 

Survey topographic quadrangle maps fill much of this 

need, at low cost; nearly all urban areas have been 

mapped. These words are surrounded by part of one: 

the Monterey, California, 7.5-minute quadrangle. To 

the urban planner and decisionmaker, topographic 

maps are useful as bases for plotting ownership, 

current land use, land-use changes, utility and 

transportation networks, and other physical, social, 

and economic information. They are also of value as 

direct planning tools for preliminary site evaluation of 

all sorts of engineering works roads, railroads, 

airports, dams, drainage facilities, industrial and 

commercial sites, pipelines, and powerlines; for 

calculating slope; for identifying obviously hazardous 

areas; for predicting where land-use conflicts may 

occur.

The Monterey quadrangle is drawn at a scale of 

1:24,000, 1 inch on the map representing 24,000 

inches, or 2,000 feet, on the ground. Each map in this 

series embraces a four-sided area bounded by 7.5 

minutes of latitude and 7.5 minutes of longitude. 

Because longitude lines in the Northern Hemisphere 

converge toward the North Pole, the quadrangles are 

not perfectly rectangular but narrow northward, so 

that those in the south cover about 70 square miles 

whereas those along the Canadian border cover only 

about 50 square miles. The 7.5-minute quadrangles 

are not even used in Alaska because they are so 

narrow. Urban areas which are not covered by 7.5- 

minute maps, including those in Alaska, are covered 

by 15-minute maps, representing four times as much 

area at about 1 inch to the mile. (Because a standard 

quadrangle requires a piece of paper about 2 feet 

square, it is impractical to reproduce entire quadrangles in this book.)

On the Monterey sheet, as on all standard 

quadrangles, water features streams, lakes, ponds, 

springs, swamps, the ocean are shown in blue; 

woodlands in green; the main works of man 

buildings, most roads, railroads, airports, powerlines, 

canals, aqueducts, piers in black. Major highways 

are in red. Urbanized areas, where there are too many 

buildings to show individually, are shown in pale red, 

except for landmark buildings such as schools, 

courthouses, and churches. These features are 

familiar to almost everyone. Not so familiar, perhaps, 

are the brown lines. These are contour lines, which 

show the shape of the land by joining points of equal 

height above sea level. On the Monterey quadrangle, 

the contour interval the vertical distance between 

contours is 20 feet. (In flatter country the contour 

interval is 5 feet or 10 feet.) In steep areas, such as the 

Santa Lucia Range at the south (lower) edge of the 

map, the contours are close together; in flatter areas, 

such as Carmel Valley near the center, they are far 

apart. In smooth terrain, they sweep smoothly along; 

in rough terrain, they wriggle. The elevation of any 

point not on a contour can be estimated from the 

elevations of the contours above and below it. In 

addition to the brown land contour lines, the 

Monterey sheet shows the depth of ocean water, in 

fathoms, by blue contours.

Standard quadrangle maps do not serve all urban 

base map needs. Some management concerns at the 

city or county level water supply, flood control, 

waste disposal, recreation may involve hundreds or 

thousands of square miles, and accordingly need 

topographic maps at smaller than quadrangle scales, 

on pieces of paper of manageable size. Practical scales 

for such uses might be 1:100,000or 1 :125,000, in which 

1 inch represents about 1.5 or 2 miles, but such 

topographic maps exist for only a few areas. (A 

1:100,000 map is used as a base in the "Front Range 

Urban Corridor" chapter.) The whole country is 

covered by Geological Survey 1:250,000 topographic 

maps, about 4 miles to the inch, but the detail on them 

is either not sufficient or not appropriate for many 

managerial needs. At the other end of the spectrum 

are site or project maps, which must show many more 

features than is possible at 2,000 feet to the inch; such 

maps, at tens or hundreds of feet to the inch, are not 

available from the Geological Survey, but must be 

obtained commercially. For readers unaccustomed to 

using topographic maps, more about such maps 

appears on the page after next.

SCALE 1:24000

1 KILOMETER
Updating 

topographic maps

Because everything on Earth changes, no topographic map is useful forever. In unsettled interior 

parts of the country, the useful life of a topographic 

map may be 50 years or more, but it is much shorter 

where natural process are very active, as along rivers 

and coasts or where man is changing the landscape by 

excavating and building. The Florida example below 

is spectacular but far from unique. In hundreds of 

urban areas, growth is so rapid that topographic maps 

become out of date within a few years. The 

Geological Survey attempts to update urban maps on 

a 5-year basis (more than 900 were revised in 1975), 

usually by overprinting revisions in purple on the 

original map, but cannot keep up with the demand. 

For example, the Monterey quadrangle on the 

opposite page was originally printed in 1947; the area 

became urbanized in the 1960's and the map was 

revised in 1968, requiring plenty of purple ink. And 

now (1977) another revision is overdue.

For planning purposes, topographic maps can be 

updated by supplementing them with recent aerial 

photographs at the same scale, the procedure used in 

Survey revision. But it is not easy to do this with the 

raw photographs, because everything on them, 

except at the very center, is displaced optically. A 

photomechanical way has been found to correct this 

distortion, and the Geological Survey recently began 

producing standard 1:24,000 orthophotoquads, 

which consist of a black-and-white photograph that is 

nearly free of distortion, in 7.5-minute format. These 

words are printed on part of one, which matches the 

Monterey quadrangle and serves as an interim 

revision map.

Unfortunately, orthophotoquads are not yet available for many urban areas. Because they are quickly 

made and accurate, orthophotoquads are in great 

demand as interim maps for those areas that have 

never been mapped at the 1:24,000 scale. These 

include about 30 percent of the conterminous United 

States, mainly rural. At the present time (1977), the 

production capacity for orthophotoquads is monopolized by interim maps. Soon, however, it is expected 

that national interim coverage will be completed and 

that urban orthophotoquads will come into volume 

production.

iPOMPANO,. BEACH
Reading and obtaining 

topographic maps

On the upper right corner of this page is a bird'seye view of a river valley flanked by hills; beneath it is 

a topographic map of the same scene. Study of the 

view and the map may be helpful to readers who are 

not accustomed to using topographic maps. The river 

flows into a bay which is partly enclosed by a sandspit. 

On both sides of the valley are flatlands into which 

small streams have cut gullies. The hill on the right, 

more than 280 feet above the water, rises smoothly 

and gradually above a wave-cut cliff. The hill on the 

left, not quite so high, rises to a steep slope from 

which it falls off gently to form a smooth sloping 

surface cut into by a few small gullies. At the foot of 

the right-hand hill, 15 feet higher than the bay, are a 

school and two houses. An unimproved dirt road and 

a bridge connect the small settlement with an 

improved light-duty road, across the river, which 

follows the seacoast and curves up the river valley.

The map shows these features by standard symbols 

and colors. The works of man school, houses, 

roads are in black; the unimproved road is shown 

by double broken lines, the improved road by solid 

ones. Water features the river and its tributaries, the 

bay and ocean are in blue. And the shape and 

elevation of the land surface are shown by contour 

lines lines of equal elevation above the sea in 

brown. The vertical difference, or interval, between 

the contour lines is 20 feet. For easier reading, some 

contour lines are numbered and the 100-foot 

contours are drawn with heavier lines. The elevation 

of any point not on a contour can be estimated from 

the contours above and below it; the school, for 

example, is between the zero contour (sea level) and 

the 20-foot contour but is much closer to the 20-foot 

contour; so, its elevation must not be far from 15 feet.

The contour lines are artificial, of course, but they 

are an effective way to represent the third dimension 

on flat paper. The shoreline is a contour representing 

zero elevation, based on mean sea level. If the sea 

should rise 20 feet, the new shoreline would trace out 

the 20-foot contour; 20 feet more of rise would 

produce the 40-foot contour, and so on. With 

practice and imagination, planners and decisionmakers can visualize clearly the land and water forms 

shown on topographic maps and apply these insights 

to their work.

Contour lines are useful for showing many things 

besides the shape of the land. Almost any kind of 

earth-science information can be portrayed as a 

contour map; the method is especially suited to 

generalizing data from specific points on the ground 

such as that from boreholes for water, oil, or minerals. 

Buried surfaces can be shown either by contouring 

their elevations above or below sea level, or any other 

level, or by contouring the depth of burial. Variations 

in the thickness of exposed or buried features can be 

well shown by contours. Such information can in turn 

be used to help make many kinds of planning 

decisions. Many examples of contour maps and their 

uses appear later in this book.

Topographic maps may be obtained directly from 

the Geological Survey or from commercial dealers, of 

which there are more than 1,550 throughout the 

United States. Indexes showing published maps for 

each State (and for Puerto Rico, the Virgin Islands, 

Guam, American Samoa, and Antarctica as well) are 

available free on request, by mail or over-thecounter. For areas east of the Mississippi River, 

including Minnesota, Puerto Rico, and the Virgin 

Islands:

Branch of Distribution 

U.S. Geological Survey 

1200 South Eads St. 

Arlington, VA 22202

For areas west of the Mississippi River, including 

Alaska, Hawaii, Louisiana, Guam, and American 

Samoa:

Branch of Distribution

U.S. Geological Survey

Box 25286

Federal Center

Denver, CO 80225 

Or for residents of Alaska:

Distribution Section

U.S. Geological Survey

310 First Avenue

Fairbanks, AK 99701

The indexes list all published maps and include order 

blanks showing prices and detailed instructions for 

ordering from the Survey. They also list addresses of 

local map reference libraries, local map dealers, and 

Federal map distribution centers.

Orientation, scale, detail, and accuracy of maps

State Teachers 

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To use maps well, one must always be conscious of 

their orientation, scale, detail, and accuracy. To read 

any map it must be oriented, placed in its correct 

relation to the Earth. This is a simple matter for all 

topographic maps, orthophotoquads, land-use and 

land-cover maps published by the Geological Survey, 

and for nearly all of its other maps as well: North is at 

the top of the sheet, south at the bottom, east at right, 

west at left. All the maps in this book are oriented with 

north at the top. Rarely, Survey maps of irregular 

shape are printed with some other orientation, as are 

maps from other sources. The orientation of virtually 

every map is shown by an arrow, or similar symbol, 

pointing north or, rarely, in another cardinal 

direction (south, east, or west). The first step in 

reading any map, then, is to check its orientation.

To illustrate scale, detail and accuracy, we will use 

topographic maps, but what we have to say applies to 

all types of maps.

Above are segments, each the same size, from three 

different topographic maps around a town called 

Gorham. The left-hand map is almost filled by the 

town, which it shows in considerable detail, including 

streets, public buildings, and even individual houses. 

This map is at 1:24,000 scale, in which 1 inch on the 

map represents 24,000 inches, or 2,000 feet on the 

ground, the same scale as the Monterey quadrangle 

and orthophotoquad. The entire map portrays 1 

square mile.

In the middle map Gorham occupies the center 

only, and there is space to show the surrounding 

country, access roads, outlying houses, a cemetery, 

and so on. There is also space to show the streets and

landmark buildings of the town, but not individual 

houses, which are indicated collectively by the red 

overprint. This map is at 1:62,500 scale, in which 1 inch 

on the map represents 62,500 inches, or about 1 mile 

on the ground. Covering 63/4 square miles, it shows a 

much larger area than the left-hand map, but in much 

less detail. This map could be enlarged photographically until 1 inch equalled 2,000 feet, as in the 

left-hand map, but the amount of detail on it would 

be no greater than before; moreover, its accuracy 

would be even less than before because of distortion 

during the enlargement process and because all the 

lines on it would be 27/$ times thicker and therefore 

take up l}/2 times as much space. Enlarging a map may 

make it easier to work with but does not improve 

either its detail or its accuracy.

The right-hand map shows Gorham at a scale of 

1:250,000, in which 1 inch represents nearly 4 miles. 

This map shows 107 square miles, and on it Gorham 

is a red-tinted blob criss-crossed by roads; enlarged 

from this map photographically to 1 :62,500 or 1:24,000 

the town would still be only a blob.

What can be said about the accuracy of these maps? 

It is natural to equate detail with accuracy, to assume 

that the more detail a map has, the more accurate it is. 

Put this way, the 1:24,000 left-hand map is the most 

accurate, the 1:250,000 right-hand map the least. But 

this is true only if the maps are made with equal care 

and from equally good information. For example, a 

careless mapmaker working on the 1:24,000 map 

might have placed a school symbol on the wrong 

building, with the result that the 1 :62,500 map would 

be more accurate, more nearly correct.

<:

But maps after all are only miniature and symbolic 

representations of reality, even at much larger scales 

than 1:24,000, and their accuracy might better be 

thought of as a measure of the care or precision of the 

entire mapmaking process, including obtaining, 

measuring, recording, and printing the information 

displayed. In this sense, all three of the Gorham maps 

are equally accurate, for all three comply with 

national accuracy standards, which require that the 

horizontal position of 90 percent of well-defined 

features must be plotted on the map within onefiftieth of an inch of their true position. But onefiftieth of an inch on paper represents different 

distances on the ground, depending on scale: it is 40 

feet at 1:24,000 scale, about 100 feet at 1:62,500, and 

about 400 feet at 1 :250,000. Similarly for elevations, 90 

percent of which, to comply with national standards, 

must be correct within one-half the contour interval, 

which is ordinarily 10 or 20 feet for 1:24,000-scale 

maps, 40 or 80 feet for 1 :62,500 maps, and 200 or 500 

feet for 1:250,000 maps. Looked at this way, accuracy 

is a relative matter. This helps explain why 1:24,000 

maps, even if greatly enlarged, will not do for site or 

project planning: Being correct within 40 feet 

horizontally and 5 or 10 feet vertically is just not close 

enough. A more important reason, however, is that 

1:24,000 maps simply do not have enough information.

Another aspect is that large-scale maps, requiring 

more detail to reach standard accuracy, cost much 

more to prepare. As a rule-of-thumb, the cost rises 

proportionately to the scale.
Land-use and f

land-cover

maps

SCALE 1:100000

1 2 3

MONTEREY 

QUADRANGLE

Topographic maps offer a great deal of information 

about the land surface, but they do not give much 

specific or detailed information about the way man 

uses the land land use or about the vegetation that 

covers the surface land cover. Such information is 

needed by planning, public works, and development 

agencies at all levels of government, as well as by the 

private sector. Thus, nearly all local governments 

have prepared their own land-use maps, using the 

standard topographic quadrangle maps or larger 

scale low altitude aerial photographs as a base. Most 

agencies have independently developed their own 

land-use and land-cover classification systems, based 

on local needs, or use one of a variety of systems 

developed by planners.

The increasing involvement of State and Federal 

agencies in managing land, water, and resources has 

made systematic land-use and land-cover mapping of 

the United States necessary and a uniform classification system for such mapping desirable. Such a system 

has been developed by the U.S. Geological Survey in 

consultation with many other Federal and State 

agencies. It is described in U.S. Geological Survey 

Professional Paper 964, "A Land Use and Land Cover 

Classification System for Use with Remote Sensor 

Data," by James R. Anderson and others (1976). In 

1975, the Survey began systematic coverage of the 

United States at scales of 1:100,000 (about V/2 miles to 

the inch) and 1:250,000 (4 miles to the inch).

The classification system recognizes the possible 

use of four or more levels of detail. Level 1 consists of 

highly generalized coverage at a small scale, which 

can be based on interpretation of Landsat satellite

Land use and land cover classification system for use with remote sensor data

Level I Level II

1 Urban or 11 Residential.

built-up 12 Commercial and services, 

land 13 Industrial.

14 Transportation, communications, 

and utilities.

15 Industrial and commercial complexes.

16 Mixed urban or built-up land.

17 Other urban or built-up land.

2 Agricultural 21 Cropland and pasture.

land 22 Orchards, groves, vineyards, nurseries, and 

ornamental horticultural areas.

23 Confined feeding operations.

24 Other agricultural land.

3 Rangeland 31 Herbaceous rangeland.

32 Shrub and brush rangeland.

33 Mixed rangeland.

4 Forest land 41 Deciduous forest land.

42 Evergreen forest land.

43 Mixed forest land.

imagery. Level II mapping, which can be based on 

high-altitude aerial photographs, is usually presented 

at intermediate scales (1:100,000 or 1:250,000) and 

allows more detailed coverage. Levels III and IV 

mapping, which use lower altitude photographs at 

large scales, are usually done only by local governments and include much detail acquired on the 

ground. The accompanying table shows the categories used for Level I and II coverage.

The map on this page is an example of Level II 

coverage for the Monterey Peninsula, the same area 

used in the preceding examples. At a scale of

Level I Level II

51 Streams and canals.

52 Lakes.

53 Reservoirs.

54 Bays and estuaries.

61 Forested wetland.

62 Nonforested wetland.

7 Barren land 71 Dry salt flats.

72 Beaches.

73 Sandy areas other than beaches.

74 Bare exposed rock.

75 Strip mines, quarries, and gravel pits.

76 Transitional areas.

77 Mixed barren land.

8 Tundra 81 Shrub and brush tundra.

82 Herbaceous tundra.

83 Bare ground tundra.

84 Wet tundra.

85 Mixed tundra.

9 Perennial 91 Perennial snowfields. 

snow or ice 92 Glaciers.

1:100,000, it covers a much larger area than the 

topographic map at 1:24,000. The map shows that a 

wide range of urban land uses and rural land cover 

exists on the peninsula.

Although the land-use and land-cover mapping 

program is new and coverage is as yet widely 

scattered, such maps are available for many parts of 

the United States. For further information on these 

maps, contact Geography Program, Land Information 

and Analysis Office, U.S. Geological Survey, MS 710, 

Reston, VA 22092.
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Their nature and 

urban uses

Topographic maps, orthophotoquads, and land- V 

use and land-cover maps are valuable tools for urban 

planning and decisionmaking, but their use is limited 13 

because they give information only about the land 

surface. Nearly all land uses involve at least the 

materials just below the surface, and most involve the 

upper 30 or 40 feet; some go much deeper: Water 

wells in arid country may go down a thousand feet or 

more as do many mine workings. Useful information 

about what lies beneath the surface begins with 

geologic maps.

Geologic maps are portraits of the earth. These 

words are printed on part of a typical one, the nowfamiliar Monterey quadrangle. Like good portraits, 

geologic maps show not merely the faces of their 

subjects but also reveal something of their inner 

nature. Wherever possible, they are compiled and 

printed on topographic maps, not only for accurate 

location but also because landforms are largely 

controlled by the underlying rocks and their 

structures, so that topography provides many clues to 

what is underneath. Geologic maps show the Earth's 

face by delineating the characteristics and distribution of exposed rocks and loose surface materials. 

They make it possible to infer the Earth's "inner 

nature" the size, shape, and position of rock masses 

and any mineral deposits, fluids, or openings they 

may contain by means of symbols. The "inner 

nature" is commonly interpreted with the help of 

slices, or cross-sections, made by combining surface 

observations with whatever subsurface information 

may be at hand from drill holes, mine workings, caves, 

or geophysical measurements. A slice through the 

Monterey quadrangle from points A to B appears 

on the opposite page. With the aid of slices in several 

directions, the geology of a block of country can be 

visualized (see opposite page) in as much detail as 

the scale of the mapping permits.

Geologic maps together with cross-sections might 

then be thought of as models of the Earth's skin, 

rather than as portraits. But geologic maps are not 

only models of space but also models of time. The

«P

history of a map area can usually be reconstructed 

because the relative ages of rock units can nearly 

always be determined, and even their ages in years 

can be estimated if they contain certain naturally 

radioactive elements which decay at known rates. 

Such reconstructions, sometimes going back billions 

of years, are often of practical, as well as cultural, 

value: Plotting the pathways of meltwaters from 

glaciers that disappeared tens of thousands of years 

ago has led to the discovery of immense reservoirs of 

underground water in the Middle West; recognition 

of caves eroded 250 million years ago in ancient 

limestone has led to the discovery of great oil pools in 

the same region.

Carrying so much information, geologic maps are 

infinitely more complicated than topographic maps. 

To use a topographic map, anyone who can read a 

road map or an atlas must master only two new 

ideas the contour line and the contour interval. But

geologic maps represent a whole new realm of 

information, thought, and experience, not to be 

conveyed in a page or two. Some idea of the 

complexity of geologic maps may come from ^ 

realizing that rocks, once formed on the ocean ,/V 

floor, on river floodplains, beneath glaciers, or 

around and below volcanoes can be eroded away; 

lifted or lowered thousands of feet; folded into 

troughs, basins, arches, domes, and far more intricate 

shapes; broken by great fractures and dragged or 

pushed hundreds of miles from their place of origin; 

furthermore, the Earth has been actively engaged in 

making, deforming, eroding, and remaking rocks for 

more than 4.5 billion years. All of this data and more 

can be condensed into symbols, colors, and patterns 

on geologic maps. Making geologic maps, or 

understanding geologic maps made by others, and 

translating them into practical terms requires many 

years of training.

SCALE 1:24000

*

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ljL_

20

1

1

1 KILOMETER

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We cannot make instant geologists of our readers, 

and we will not try. Nowhere in this book do we tell 

how to read geologic maps, though we list a few 

references that do tell. But it is important for urban 

planners and decisionmakers to be aware of the basic 

maps and sections needed for successful application. 

Once a geologic map exists, information*relevant to 

some urban situation can be extracted from it, 

translated into relevant terms, and put to use, 

sometimes alone but more often in conjunction with 

other maps and information. Much of this book 

consists of maps that have been abstracted, translated, or derived from geologic maps. Some of the 

geologic maps themselves have been included, not 

with the thought that many readers will be prepared 

to use them directly, but as a constant reminder that 

the underlying geologic facts and inferences are an 

essential base for sound land-use and resourcemanagement decisions.

DESCRIPTION OF MAP UNITS

SURFICIAL SEDIMENTS 

Beach sand 

River sand and gravel

Dune sand 

Alluvium 

LANDSLIDE DEBRIS-may be actively moving

OLDER SURFICIAL SEDIMENTS

Older alluvium and terrace gravel and sand 

Marine terrace sand and gravel

MONTEREY SHALE Siliceous marine deposit 

Siliceous shale,light-brown to white 

Semi-siliceous shale, yellowish-brown

MARINE SANDSTONE

Sandstone, buff to 1 ight-gray, upper part

Volcanic rocks

Sandstone as above,lower part

CARMELO FORMATION OF BOWEN (1965) 

sandstone, siltstone, mudstone, and conglomerate 

Cobble and boulder conglomerate, mostly granitic

GRANITIC ROCKS Light-gray crystalline rocks 

Granodiorite, porphyritic 

Granodiorite

Contact 

Dashed where approximately located,

gradational, or concealed 

U ___mmu

D Fault

Dashed where inferred;dotted where concealed. 

U, relatively upthrown side; D.downthrown side.

Thrust fault

Dashed where inferred; dotted where concealed. 

Sawteeth on upper plate

.20 60

Horizontal Inclined Vertical Overturned

Strike and dip of beds

Direction of 

dip from distant view

Anticline Syncline

Fold axis, showing direction of dip of limbs 

and of plunge. Dotted where concealed

Direction of 

landslide 

movement

Abandoned exploratory 

well drilled for oil 

or gas, showing total 

depth in feet

Y

Water well

Quarry Spring 

Some symbols do not appear on that part of the map shown opposite

Reading and obtaining geologic maps, 

cross-sections, and block diagrams

Geologic maps, slices (cross-sections) through the 

area they represent, and block diagrams constructed 

from the maps and cross-sections are basic tools for 

viewing the materials of the earth and their relations 

to each other. Concealed in their technical words and 

symbols is a wealth of information useful to urban 

planning and management. Geologic maps have 

many common characteristics, regardless of scale; 

some of these are exhibited on the map of part of 

the Monterey 7.5-minute quadrangle on the opposite page. Covering the same area as the Monterey 

topographic quadrangle and orthophotoquad on 

preceding pages, the geologic map is far more 

complicated.

The boxes in the "Description of Map Units" show 

the colors, patterns, and letter symbols assigned to 

each map unit, which is briefly described. This part of 

the map has 16 units, arranged in order of relative age 

(oldest at bottom); the whole map has 27. Some 

quadrangle maps have 50 to 60 units; regional or 

State maps may have a hundred or more.

The symbols below the boxes give additional 

information. Most of it is about the structures in the 

rocks, which may range from the alinement of grains 

or layers visible in a hand specimen (not noted on this 

map) to the direction and inclination of layers in large 

natural or manmade exposures ("strike and dip of 

beds") and to giant bends or folds ("anticline," 

"syncline") or long and deep breaks in the rocks 

("fault," "thrust fault") measurable in miles. Other 

symbols convey information about landslides, minerals, fuel, construction materials, and water resources (the bottom row of symbols to the left for 

the Monterey map).

Cross-sections, or slices, through the mapped area, 

like the one at the bottom of this page, give an 

idea of the third dimension. Often, the vertical 

scale on cross-sections is exaggerated for easier 

viewing. This leads to some distortion, which should 

be kept in mind.

Finally, map and cross-sections can be combined 

into three-dimensional sketches or block diagrams, 

like that below, to create a sense of realism. The 

diagram shows the same area as the page-size map

but is reduced to about one-fifth the scale, 1 :125,000. 

So much detail must be omitted at this scale that it 

takes a while to realize we are viewing the same area. 

The omitted map units are mainly of loose surface 

materials. Although patchy and thin, these materials 

may be very significant for site planning and development another demonstration of the importance of 

map scale to urban application.

Finding out what geologic maps are available is not 

as simple as tracking down topographic maps, 

because geologic maps have many sources. They are 

produced not only by geologists of the U.S. 

Geological Survey but also by geologists of State 

geological surveys, by teachers and graduate students 

at many collegiate institutions, and by private 

companies and consultants. Indexes to all published 

geologic maps in each State, updated every few years, 

can be obtained free on application to the Geological 

Survey offices listed three pages back. Many usable 

maps, however, are never published, and of course 

recently published maps are not yet listed. The best 

guide to unpublished or newly published local maps 

is the appropriate State geological survey or its equivalent, and the District and Public Inquiries offices of 

the U.S. Geological Survey, listed on pages 90-91. 

Geology or earth-science departments in nearby 

universities and colleges can also be helpful.

Unfortunately, basic geologic maps at large scales 

are not available for many urban or urbanizing areas. 

Most existing mapping has not been in or near cities, 

but rather in remote areas that have mineral or fuel 

potential or are of scientific interest. Nor is much new 

geological mapping being done: Mapping at scales 

of 1:100,000 or larger is now proceeding at the snaillike pace of 30,000 to 40,000 square miles per year, 

most of it far from cities. More than half of this 

mapping is by the U.S. Geological Survey, which 

conducts as much as its staff and funds permit. The 

bulk of the remainder is by State surveys.

Geologic mapping, unlike modern topographic 

mapping, cannot be done largely indoors from aerial 

photographs but requires intensive field work. Only a 

few useful properties of rocks can be measured on 

photographs, and even these are often obscured by 

soil, vegetation, or the works of man. Producing 

geologic maps is therefore rather slow and expensive: 

Mapping at 1:24,000 scale, and related laboratory and 

office work, typically proceeds at a rate of about 50 

square miles per mapper per year, at an overall cost of 

about $1,500 per square mile; at 1:100,000 scale, the 

rate is about five ti mes faster and the cost decreases to 

around $200 per square mile. However, when 

geologic maps are well done at suitable scales, they 

do not go out of date quickly, so the investment 

required can be amortized over a long time. Plainly, 

acquiring geologic mapping as planning information 

for large urban areas requires understanding, foresight, and commitment.

HORIZONTAL SCALE 1:125,000 

VERTICAL EXAGGERATION X2

(Adapted from California Division 

of Mines and Geology, 1959)

SEA LEVEL

-600'

HORIZONTAL SCALE 1:24,000 VERTICAL EXAGGERATION X2

 SEA LEVEL

- 600'
Hydrologic maps

Hydrologic maps portray the occurrence of water 

on and beneath the land surface. They are useful to 

planners and managers in evaluating water supply, 

water-related hazards such as flooding and high 

hydrologic maps exists; so great, in fact, that it is 

not practical to show representative examples in this 

practical to show representative examples in this 

"Introduction." Numerous examples of hydrologic 

maps appear throughout this book. Among them are 

maps showing drainage areas, maps showing the 

depth to ground water and the thickness of waterbearing formations, maps depicting the quality of 

water, and maps showing the predicted water-level 

declines which would result from increased pumping 

of ground water. The full range of hydrologic maps is 

seldom available for any given area.

One type of hydrologic map the flood-prone area 

map is widely available and is illustrated here. More 

than 12,500 of these maps have been prepared by the 

U.S. Geological Survey, covering virtually all the 

developed and developing parts of the nation. Still to 

be mapped, however, are many areas of potential 

future development, public lands for which planning 

and management decisions are needed, and recreational lands. Flood-prone area maps have been used 

in making many decisions regarding uses of land 

subject to flooding. Among the most widespread and 

important uses are in the National Flood Insurance 

Program.

Flood-prone area of Agua Caliente Wash and Tanque Verde 

Creek, Arizona (1957)

SCALE 1:24000

o 1 MILE

1 KILOMETER

Flood-prone area maps made by the Survey show 

on a standard 7.5-minute quadrangle base the 

approximate boundaries of the "100-year flood" 

the area that has a 1 percent chance of being flooded 

in any given year. They are available free of charge 

from the District Offices listed on pages 90-91. These 

maps are generalized. More detailed flood-hazard 

maps, prepared by such agencies as the Army Corps 

of Engineers, the Soil Conservation Service, private 

consultants, and also the Geological Survey, are 

available for some areas.

Part of a typical flood-prone area map, from 

suburban Tucson, Arizona, is at the upper right. The 

area in blue has a 1-in-100 chance, on the average, of 

being inundated during any given year; rarely, even 

larger floods than that illustrated may occur, 

inundating additional areas. The small areas that may 

be inundated by floods on minor streams are not 

shown.

When the topographic map was made, in 1957, the 

flood plains of Agua Caliente Wash and Tanque 

Verde Creek were only sparsely developed, with a 

few roads and widely separated buildings. Since then, 

more roads and many more houses and industrial 

structures have been built within the flood-prone 

area, as the recent aerial photograph of the same area 

shows (below) endangering more lives and property.

Recent and established residential development in the 

flood-prone area of Agua Caliente Wash and Tanque Verde 

Creek, Arizona (1973)

Photograph by Cooper Aerial Survey Company

10
APPLICATIONS IN A PACIFIC

C

tf 

ount

Land-use-controls arising from **yt *- s -

bf_ seacliffs, landsliding,

d fail . Wv. ' «r..*v2sv :>» ^ .:.

y Brian Atwater
123° 122°

0 10MILES

H-H

0 10 KILOMETERS

Central San Mateo County

The subject area is outlined in 

yellow on the aerial photograph 

(left) and on the index map 

(right).

I I *Uf~/ 

Geologic processes and land-use controls

Failure to recognize and adjust to geologic 

processes in California has cost approximately 1,000 

lives and $10 billion in property damage (1970 dollars) 

during the past 125 years. The threat of even greater 

losses in the future has caused the legislature to 

require local government authorities to incorporate 

geologic information into land-use plans and decisions. This chapter describes the geologic basis for 

several land-use regulations and guidelines in San 

Mateo County, which is just south of San Francisco 

(see index map above, right).

Geologic processes that have evoked governmental controls in this county include erosion of 

seacliffs and beaches, landsliding, movement along 

faults, deformation of water-saturated clay and sand, 

flooding of coastal areas by earthquake-induced sea 

waves, flooding from surface runoff, and intrusion of 

seawater into fresh-water aquifers. Public policies 

and ordinances, as of 1977, that pertain to the first

three of these processes erosion of seacliffs and 

beaches, landsliding, and fault movement are 

summarized at the top of the facing page and 

discussed in greater detail in the rest of the chapter. 

Regulations and guidelines that incorporate new 

geological information will no doubt supersede these 

ordinances from time to time.

The critical first step toward avoiding or minimizing 

loss of life and property due to geologic processes is 

to determine the location of potential hazards such as 

faults and unstable slopes. Much of this information 

can be obtained or derived from aerial photographs and from earth-science maps, as this chapter 

illustrates.

The capacity of land to support human uses 

depends partly on topography, the shape of land 

surface. Thus, most of the people in San Mateo 

County live on the plain and foothills bordering San 

Francisco Bay and on lowlands along the Pacific 

Ocean, but relatively few inhabit the rugged

mountains in between (note distribution of urban 

areas on aerial photograph above). The block 

diagram on the facing page sketches these landforms 

but greatly exaggerates their vertical dimensions; the 

shape of the land is depicted much more accurately 

by contour lines on topographic maps. A small-scale 

(1:125,000) topographic map is the base for the 

various maps of central San Mateo County shown 

here and later in this chapter.

The capacity of the land to support human uses also 

depends on the physical properties and distribution 

of earth materials. The distribution of various kinds of 

rocks and sediments and the location of structural 

features such as faults in central San Mateo County 

are shown on a geologic map at the bottom of this 

page. The area of the map is outlined in yellow on 

the index map and the aerial photograph (above). In 

the block diagram opposite, the front and right sides 

are vertical slices through or cross sections of the 

southern and eastern margins of this area.

Geologic map of central San Mateo County

12
GEOLOGIC 

PROCESS

Erosion of cliffs and beaches along the Pacific Ocean Landsliding in hillside areas Displacement of the ground surface along active faults

PUBLIC 

POLICY

Discourage development of unstable shoreline areas Discourage development of unstable slopes Discourage development in active fault zones

PUBLIC Prohibit or restrict construction of buildings within 

ORDINANCE certain setbacks from unstable seacliffs

Restrict density and type of development where 

slopes are unstable or steep

Prohibit or restrict construction of buildings for 

human occupancy in active fault zones

Some land-use controls in San Mateo County arising from geologic processes

Geology of central San Mateo County in three dimensions

SAN FRANCISCO BAY SEDIMENTS

Soft mud with shells, peat, and sand. Covered with manmade 

fill in many areas

LANDSLIDE DEBRIS 

Masses of rock and soil moved downhill by gravity

STREAM AND BEACH SEDIMENTS 

Gravel, sand, silt, and clay. Locally interlayered with 

San Francisco Bay sediments

YOUNGER SEDIMENTARY ROCKS 

Sandstone and mudstone. Locally includes volcanic rocks

GRANITE

Locally includes metamorphic rocks

OLDER SEDIMENTARY AND IGNEOUS ROCKS 

Sandstone, mudstone, altered igneous rocks, and scarce limestone

FAULT

Solid line where location is well-known, dashed line where location is 

approximate, and dotted line where location is concealed. Query indicates uncertainty about existence of fault

BOUNDARY BETWEEN DIFFERENT KINDS OF EARTH 

MATERIALS

13
Erosion of seacliffs 

and beaches

The coastal areas of the United States are narrow in 

extent but broad in human significance. Most 

Americans depend directly or indirectly on coastal 

lands and waters for recreation, industrial and 

commercial activities, waste disposal, food production, and natural preserves. In addition, more than 

half the Nation's people live within 50 miles of the 

ocean or the Great Lakes, and the percentage is 

increasing.

Recognition that coastal resources are finite, that 

claims on them are often competitive, and that some 

claims are broader than local has led several States to 

assume legislative authority over development of 

their coastal areas. These problems have also 

prompted the Federal Government to fund coastalzone planning by State governments under the 

Coastal Zone Management Act of 1972. As a result 

California has adopted a comprehensive plan for 

resource use in the coastal zone. Mandated by a 

Statewide referendum in 1972, this plan was ratified 

by the State legislature in 1976. The principal policies 

of the plan are to guarantee public access to the 

shore, to insure that coastal developments serve the 

public as a whole, to protect and restore coastal 

marshes, to preserve coastal farmlands, and to provide stringent environmental safeguards for coastal 

developments, particularly energy facilities. These 

policies are to be implemented by local governments, which are required to adopt them as part 

of their own general plans.

California's coastal zone plan recognizes erosion of 

seacliffs as one of several geological processes that 

can endanger human life and property in coastal 

areas. Battered by waves and rain, many seacliffs in 

California have retreated during historic time, as 

shown in the photograph (right). Rapid erosion of 

developed cliffs has led to loss of property and to the 

building of protective structures. Because protective 

structures are costly and may cause esthetic, environmental, engineering, and legal problems, the State 

plan limits construction on or near cliffs that might 

eventually require such works. The regulations 

permit development only if the setback from the 

edge of the seacliff is adequate to assure integrity of 

the structure for its expected economic lifespan. In 

addition, site stability must be demonstrated for an 

area that includes the base, face, and top of all cliffs or 

bluffs more than 10 feet high.

In San Mateo County, State guidelines for bluff-top

Unsightly boulders temporarily guard this structure, 

built near El Granada in 7973, from further battering 

of storm waves. Continued bluff retreat at historic 

rates (see middle map on opposite page) will require 

additional protective measures or lead to demolition 

of the building within the next few decades. County 

regulations (top map on opposite page) will prevent 

or reduce future damage to property and scenery 

by controlling development near unstable seacliffs.

development have been adapted and refined to 

include information on historical bluff erosion 

(middle map on opposite page), resistance of bluff 

materials to erosion (bottom map opposite), and 

degree of natural protection from waves. This

combination of historical and geological data has 

permitted coastal bluffs to be divided into three 

stability categories with corresponding development 

regulations that reflect the relative instability of the 

seacliff (top map opposite).

Man-induced beach erosion

Natural sand transport

Waves striking the shore obliquely cause 

beach sand to move parallel to the shore.

m~-,.. --*^vf,-5^ ;|fe^^:

Deposition ' /,' '^S?^L^^,,,^.n .- -^

&* &&

Je

Jetty-obstructed sand transport

Sand accumu/ates on one side of the jetty, starving 

the beach on the other side, and resulting erosion 

threatens the house.

Seacliffs dominate the coast of northern California, 

but beaches line other parts of the Pacific coast and 

much of the Atlantic and Gulf coasts. Consequently, 

movement of beach sand is more important than 

retreat of bluffs in shoreline-erosion problems of 

many coastal areas.

Man contributes to beach erosion by reducing the 

supply of beach sand and obstructing its movement 

along shore. Supply is reduced by seawalls and dams;

seawalls prevent production of sand from erosion of 

seacliffs, and inland dams prevent transport of sand to 

the ocean by rivers. Sand movement along beaches is 

commonly obstructed by jetties and breakwaters (see 

diagrams above). Jetties and breakwaters also can 

generate erosion by redirecting wave energy. For 

example, a breakwater at Half Moon Bay has 

accelerated retreat of nearby bluffs as much as 

fourfold since its construction in 1959 (see middle 

map on opposite page). Efforts to halt this erosion,

such as emplacement of riprap barriers, have failed 

in the areas of most rapid retreat (see photograph 

of undermined road on opposite page).

The State and county regulations for bluff tops 

discussed above may prevent some man-induced 

erosion of beaches. By preventing construction of 

barriers between coastal bluffs and attacking waves, 

these regulations insure continued production of 

sand from seacliffs.

14
County regulations for bluff-top development

EXPLANATION OF SETBACKS 

EX - structures excluded 

DS - demonstrate stability in 

geotechnical reports

NR - normal geotechnical 

reports for proposed 

land use

Historic bluff erosion

AVERAGE RATE OF EROSION

Greater than 1 foot 

(0.3 m) per year

SOURCES OF DATA 

Based mostly on comparison of:

(1) Aerial and ground photographs taken 1926 -70

(2) Maps made in 1850 - 1956

Supplemental information from 

other archival materials and 

from field investigations of 

manmade features, as noted 

on the map

Less than 1 foot 

(0.3 m) per year

Rate, in feet per year, at locality 

indicated by arrow

122°30' 122°15

Erosion resistance of bluff materials

MATERIAL

(See geologic ma p 

P-13)

Stream and beach

RESISTANCE

TO EROSION

Low High

Hard 

granite

Very soft stream and beach sediments

Soft marine

sedimentary

rocks

15
Landsliding

Landslides, like those shown here, are widespread 

in the San Francisco Bay region. The cost of landslide 

damage in the region was at least $25 million in the 

rainy season of 1968-69. According to the California 

Division of Mines and Geology, as much as$10 billion 

may be lost to landslides throughout California from 

1970 to 2000 unless existing policies and practices are 

improved.

Damage resulting from landslides can be reduced 

by avoiding landslide-prone areas or by removing or 

stabilizing landslide masses. The California Division of 

Mines and Geology estimates that 90 percent of 

projected landslide losses in the State could be 

avoided by applying preventive and remedial measures. The estimated cost of these loss-reduction 

measures would equal only 10 percent of the 

projected landslide losses a highly favorable costbenefit ratio.

Houses damaged by landslides 

in San Mateo County

In the upper scene, the house and several 

neighboring houses have been made uninhabitable by relatively small and undramatic downs/ope movements of the 

ground beneath them. In the scene at 

left, the ground has suddenly slid away, 

leaving the houses dangling. (Photographs 

by Earl Pampeyan.)

San Mateo County began to apply preventive 

measures in 1973 by regulating the density and nature 

of development in landslide-prone parts of remote, 

mountainous, unincorporated areas. The maximum 

residential densities allowed by San Mateo County 

are shown on the map at the top of the opposite page. 

This map is based on two maps, one of landslide 

susceptibility (simplified in the map below it showing 

identified landslides), and one of land slopes 

(bottom of page). It reflects the fact that landslides 

are more likely to occur in areas that have steep 

slopes or are underlain by preexisting landslides.

Zoning ordinances in these areas permit a maximum average density of 1 dwelling unit per 5 acres, 

but a slope-stability ordinance further restricts 

development to 1 unit per 40 acres where the land is 

underlain by landslide deposits more than 500 feet 

long. In addition, no residential structures can be 

built on landslides without detailed geologic site 

investigations and adequate engineering design. 

Finally, the county's slope-stability regulations prohibit the construction of schools, hospitals, fire 

stations, dams, and powerplants in areas underlain by 

landslide deposits.

San Mateo County's residential density regulations 

also apply to steeply sloping areas which, though not 

underlain by landslide deposits, are very susceptible 

to landsliding. Development of steeply sloping land is 

discouraged not only because of the landslide hazard, 

but also because it commonly necessitates considerable grading and alteration of the natural terrain, 

requires pumping stations for water and sewer lines, 

and contributes to erosion and flooding. Most of the 

steep lands in the county are south of the area shown 

on the opposite page.

RATIO= HORIZONTAL: VERTICAL

Categories of land slope expressed as percentages, degrees, and ratios 

(based on Nichols and Edmundson, 1975). PERCENT OF SLOPE

16
Maximum residential density allowed by San Mateo County

MAXIMUM DENSITY OF 

DEVELOPMENT. ACRES 

PER DWELLING UNIT

LIMITING 

CRITERIA

Slope 0-15 percent 

Slope 15-30 percent 

Slope 30 - 40 percent

| Slope more than 50 

J percent

I Landslide

37'30' ->

Landslides in central San Mateo County

LARGE LANDSLIDE

More than 500 feet long. Generally identified from aerial 

photographs

SMALL LANDSLIDE

50 - 500 feet long. Identified 

from aerial photographs or 

mapped on the ground. Landslides smaller than 50 feet not 

shown

Boundary of unincorporated 

lands to which the above 

regulations apply

122° 30'

(Modified from Brabb and Pampeyan,1972b)

122*15

Land slopes in central San Mateo County

17
Fault movement

Many schools, hospitals, and public and private 

structures for human occupancy in California are 

located on or near active faults (see sketch below). 

The most notorious of the many such faults is 

the San Andreas, which crosses central San Mateo 

County in its 600-mile-long path through California. 

The fault zone appears in the photograph on this page 

and is shown on the three maps opposite. Concern 

about the proliferation of structures on and near 

recently or potentially active faults led the California 

State Legislature to enact the Alquist-Priolo Geologic 

Hazard Zones Act of 1972, revised in 1975 and retitled 

the Alquist-Priolo Special Studies Zone Act. This act 

requires geologic site investigations along potentially 

hazardous faults under policies and criteria established by the California Mining and Geology Board.

The "special studies zones" are strips one-eighth of 

a mile or more wide along each side of faults recognized as active or potentially active by the State 

Geologist, within which the danger of fault rupture is 

presumed to exist until otherwise demonstrated by 

direct investigation (see top map opposite). Geologic 

reports directed at the problem of potential surface 

faulting are required by State law for all public 

structures within the "special studies zones" if faults 

have moved within the past 11,000 years and prohibits such construction within 50 feet of a fault 

which has displaced the ground surface. Site investigations may also be required by local governments 

for single-family residences, which may similarly be 

prohibited within 50 feet of an active fault.

Displacement of the ground surface along faults 

accounts for only a small part of earthquake damage. 

The most intense and widespread damage is typically 

caused by shaking of the ground at some distance 

from the active fault. Thus, the land-use regulations 

for fault zones in California are only a first step in 

reducing earthquake damage.

r x. ^. _-

Construction in the San Andreas fault zone

Some of the suburbs in this view, looking 

southeast from above Daly City, lie across 

strands of the San Andreas fault (red lines). The 

earthquake of 1906 caused as much as 8 ft of 

horizontal displacement along fault strands like 

these; much less movement would wreak 

havoc here. State laws enacted in 1972 require 

geologic investigations prior to construction 

of a public structure in the "special studies

zone" (area in orange) and prohibit building 

of public structures across the red lines. Site 

investigations may also be required by local 

governments before construction of new singlefamily dwellings. The maps on the opposite 

page show faults and "special studies zones" 

in central San Mateo County, which is outlined 

in yellow at the top of the photograph. (Photograph by R. E. Wallace.)

Kinds of fault displacement

Much of California is laced with faults surfaces in the Earth along 

which failure has occurred, so that the earth materials on opposite 

sides have moved relative to each other. The diagrams above show 

horizontal movement, the main kind of displacement along the 

well-known San Andreas fault, a small segment of which is pictured 

at the top of the page. Other faults may produce vertical movement or a combination of horizontal and vertical movement.

Although the diagrams above and the maps on the opposite page 

represent faults as simple, single breaks, most faults actually 

occupy zones which are tens to thousands of feet wide and which 

include many individual surfaces, called strands, along which 

movement has occurred. Multiple strands of the San Andreas 

fault zone are shown as red lines on the photograph above.

Known and suspected faults in central San Mateo 

County are shown on the bottom map opposite. 

Some of the faults shown on that map have not moved 

for many millions of years and thus can be considered 

inactive. Others, however, show evidence of current 

activity or have moved recently enough to be 

considered "potentially active" by the State of

Dating fault movements

California for the purposes of the Alquist-Priolo Act; 

such faults are singled out on the middle map 

opposite. They have been used as the basis for 

"special studies zones," shown on the top map 

opposite.

Faults are easy to date if they are caught in the act of 

moving. If not, only rather rough limits can be set on 

time of movement. The maximum age of an

unwitnessed or prehistoric fault movement can be 

learned if the youngest rock or soil broken by the 

movement can be dated. This rock or soil can be 

dated if it contains certain fossils or certain radioactive elements. And the minimum age can be 

determined if the fault is covered by unbroken rock 

or soil that can be similarly dated.

18
Fault hazard zones mandated by State law

SPECIAL STUDIES ZONE - Special studies are 

required before building structures for public 

occupancy. Compiled from official maps of the 

State of California as of February 1976

ACTIVE FAULT-No structures for public occupancy permitted within 50 feet of fault trace

37-301 -

(Compiled from California Division 

of Mines and Geology. 1974, 1975)

Faults that may cause displacement of the ground surface

Fault with known movement during the past 11,000 

years (defined as "active" by the State of California)

Fault with known movement during the past 2-3 

million years (defined as potentially active by the 

State of California)

Notes on map give some of the evidence 

for recency of fault movement

See bottom map for explanation of line symbols

122-30' 

(From Lawson and others. 1908, and K. R. Lajoie)

Faults of central San Mateo County

m _______ FAULTS

- Location well-known

 Location approximate

Concealed by water or younger rocks 

? * * Existence uncertain

122°30' 

(Generalized from Brabb and Pampevan,1972a)

19
20
APPLICATIONSIN AN ^Rlb'tNVIRONfvT

CLW^BURStflMFIV ;^»'V (. -/ Ti

 ^ ./*.£- V »"

 >f

'^

cso

Iling hillside development; 

rqtecting and conserving

and water resources
Hillside development

ordinance based on

slope

We have just read about the instability of steep 

slopes in the seasonally wet environment of the San 

Francisco peninsula, but even in the semiarid desert 

environment of Tucson, Arizona, slope of land is an 

important consideration in preparing sites for urban 

development. For example, some sites require cutand-fill for building pads and access roads. The 

amount of cut-and-f ill needed depends on the design 

of the structures and the slope of the construction 

site. Slope is also an important consideration for 

utilities such as sewer lines.

Constructing building pads, roads, and utility 

trenches on excessively steep slopes is not only costly 

to developers and local governments but may be 

esthetically and environmentally damaging. For 

example, the soils in many steep areas, although 

shallow, absorb precipitation, retard runoff, and 

provide a growth medium for hardy desert vegetation 

which in turn serves as both food and protective 

cover for a variety of wildlife.

To provide building pads, utility systems, and roads, 

the thin soil veneer must be scraped away, and 

extensive blasting in hard bedrock may be necessary. 

Loss of the soil veneer and vegetative cover can lead 

to an increase in runoff by a factor of three or more. 

And in the desert, rainfall, though infrequent, 

commonly is torrential. Fill and unprotected soils are 

highly susceptible to erosion, particularly on steep 

slopes. Storm runoff with its larger loads of silt and 

other debris thus results in deposition of silt which 

can increase flood hazards downstream.

Cut-and-fill techniques also tend to leave large 

visual scars. In the desert, these bare rock scars may 

exist for many decades, because revegetation is 

usually slow.

Slope maps are a valuable tool in developing and 

administering slope regulations. Slope can be calculated from a standard topographic map, but this is 

laborious in any case and is done easily only by a 

person trained in using maps. Therefore, making 

slope maps from topographic maps by a photomechanical process greatly simplifies their preparation. The map on the facing page is such a slope map 

of an area on the west side of Tucson which is 

undergoing considerable new residential and other 

urban development. A wide range of slope can be 

seen, illustrated by a few representative photographs. 

The matching part of the topographic map from 

which the slope map was made is shown on this page.

Many communities in semi-arid country have 

enacted building regulations and zoning ordinances 

based on slope in an attempt to control excessive 

runoff, siltation, and erosion; to maintain vegetative 

cover; to protect wildlife habitat; and to preserve the 

esthetic character of mountain areas. Pima County, 

which includes Tucson, has enacted such an ordinance, establishing a Hillside Development Zone.

Slope is not the only consideration which should 

be used in regulating development in hillside terrain. 

The relative stability of rock units is equally important, 

as illustrated in the preceding example from San 

Mateo County, California, and in the last example, 

from Fairfax County, Virginia. Relative slope stability 

was not considered in Pima County's Hillside Development Ordinance only because the County's building code requires fill stabilization in conformance 

with the National Uniform Building Code. The 

following excerpt from the Pima County Hillside 

Development Zone Ordinance is cited as an example 

of how one community is approaching the problem 

and not necessarily as a model for other communities 

to follow.

Topographic map of part of the Cat Mountain quadrangle (scale 1:24,000)

:*.;£ S - 

 : ' 

j i < -. i / v«r i

\;)/z v,-^..,} \

>^ 7 5y£iT"""^ ,-: Vf

$'\ f #" s' A« - F j.* * s ... f V

. ,

/ i ^.' University of Arizona , M 

/ /^'Geochronplpgy ^Laboratoriei 

xO/ " \ -^e% I "j

 ^655 'S* \k) .? I

 rM

» f / J" "I 1 .1 . / "-rtaavo ; , 11.

X ) | '^^U^fr/'/y ?/ -i^-v* "Jiv

'-:-}&" 1

- <ifivs *,7jVY'

/'JP I {

1 f /' Jf t \

~JL,:Jif^ 'r. ji^.;=.

. .

it. : * " i »"^T i r a^

""^ i' *** .*-r;v."\ * i'"-"**,

^?:1tf^ / ^^'-.-: lJLL^^--' L ^v^^j.^

SEC. 4401 GENERAL PURPOSE

OF THE

HILLSIDE DEVELOPMENT 

ORDINANCE

Whereas the hillsides of Pima County differ from the 

county's flat lands, hillsides necessitate different 

provisions for their development and their protection. The purpose of the Hillside Development 

Ordinance is to permit development on hillside areas 

while conserving and promoting the public health, 

safety, convenience and general welfare by minimizing water-runoff and soil erosion problems incurred 

in adjustment of the terrain to meet development 

needs; providing safe and convenient access to 

hillside development; conserving the unique natural 

resources of hillside areas; and maintaining the 

character, identity, and image of Pima County.

ARTICLE 44

SEC. 4402 SCOPE

HILLSIDE

The Pima County Hillside Development Zone shall 

apply to the following areas:

4402.1 All lots or parcels or any portion thereof 

containing slope zones of fifteen percent (15%) or 

greater as identified on the United States Geological 

Survey (USCS) 7.5 Minute Series Slope Maps, identified in Exhibit A of this Ordinance.

SEC. 4407 SLOPE DENSITY 

REQUIREMENTS

4407.1 For land areas within the jurisdiction of the 

HDZ, average dwelling unit density shall not exceed 

that allowed by the following table or existing zoning 

whichever is more restrictive:

22
Slope map of part of the Cat Mountain quadrangle (scale 1:24,000)

^AXX

^- j* -^" v\\ wen

x ri : VJT* . » J ._«.% * ?' ^^*

^^.j-^^'ii^.

^HtlP

- '^t^J Jf «*~i * i * ^"_ *! ; T;"T ^

DEVELOPMENT ZONE (HDZ)

Average cross slope* (%) Average lot size 

(round off to nearest whole number) (acre)

15 1.0

16 1.0

17 1.25 

18 1.37

19 1.5

20 2.0

21 2.25 

22 2.5

23 3.5

24 4.5 

25 6.0

26 7.0

27 8.6

28 10.4 

29 12.8

30 16.0

31 23.5 

32 31.0

33 and greater 36.0

 As defined in "User's Guide to the Hillside Development Zone for 

Plma County, Arizona," Pima County Planning Department, September 

1976. p. 2.

* * *

SEC. 4412 SITE CUT AND FILL

REQUIREMENTS

4412.1 The uppermost point of a cut slope shall not

be higher than the top of a structure on the same site.

4412.2 The vertical distance of exposed fills shall not

be greater than fifteen (15) feet from the natural

ground or top of the retaining wall.

4412.3 Vegetation shall be re-established on all

exposed fill slopes by the developer. Exposed graded

areas shall be mulched and seeded with a mixture of

desert grasses and desert shrubs, trees, or cacti to

provide a basic ground cover which will prevent

erosion and permit natural revegetation.

4412.4 In lieu of re-establishing vegetation on cut

and fill slopes, exposed slopes may be rip-rapped with 

stone which blends in with the natural setting.

* * *

Housing on slopes above 20 percent

Mountains: Building and construction 

problems likely to be severe; danger 

from foundation erosion, rockfalls, and 

landslides may be great.

Housing on slopes between 15 and 20 percent

Foothills of mountains and banks of 

deeply incised streams: Building and 

construction problems moderate to 

severe; special engineering practices 

may be necessary.

Housing on slopes below 15 percent 

(lot size based on existing zoning)

River floodplains to lower foothills of 

mountains: Few or no construction 

problems due solely to slope.

23
Resource protection

ordinance based on

copper potential

Eastern Pima County has yielded millions of tons of 

copper metal since commercial mining began in 1858, 

and copper mining is and will continue to be a major 

contributor to the regional economy. Past production 

and potential for other copper deposits are suggested 

by the map on the facing page.

Eastern Pima County, which includes Tucson, is also 

one of the fastest growing urban areas in the country. 

From a population of 130,000 in 1950, the greater 

Tucson area ballooned to 415,000 in 1976, and this 

rapid growth, illustrated by the map on the right, 

continues unabated. The huge embankments and 

dried ponds that are the waste products of copper 

recovery are encroaching on a satellite development 

built before large-scale mining began (see photograph); as houses spread up the hills that flank 

the basin and into the valley to the west of Tucson, 

they begin to impinge on land that may be ore 

bearing, and on the copper mines themselves.

Open-pit mining and quality housing are not 

compatible. On the one hand, housing development 

may prematurely or inadvertently occupy orebearing ground, hampering its development and its 

eventual economic contribution. As mineral rights 

are reserved to the Federal Government, and mineral 

lands, even if the surface is privately owned, are open 

to mining claims, the potential for conflict is great and 

inevitable.

Growth near Tucson, 1957-71, 

illustrated by part of the Tucson 

East quadrangle (at scale of 1:48,000)

The map, prepared in 1957, was photorevised in 7977. /Areas shaded purple 

became urbanized between 7957 and 

7977. Updating to the present would 

show much more urbanization.

CARPORTS

... a county that won't stop growing

On the other hand, the waste products of largescale mining are often a nuisance and sometimes a 

safety or health hazard. The pits and appurtenant 

waste-rock dumps may occupy several square miles. 

Concealing the dumps is difficult because of the time 

and cost needed to reestablish vegetation on them. In 

addition to the visual intrusion, the dumps are a 

source of windblown sediment; and the highly 

mineralized water used to transport the fine-grained 

waste rock may degrade ground water, the only 

source of public supply for Tucson. Use of the 

adjacent land for farming or industrial purposes, 

rather than for housing, is less troublesome but 

results in competition for the limited ground-water 

supply.

Abandoned open-pit workings or underground 

workings with surface openings may become serious 

hazards if urbanized. The openings may be too large 

to fill with waste rock, or to render less hazardous in 

other ways at justifiable cost.

The Board of Supervisors of Pima County, after 

considering the problem at length, decided that the 

first step should be to protect the resource. Fortunately, the U.S. Geological Survey, building on many 

decades of regional and detailed mineral resource 

examination and mapping, had released two maps 

showing, in a preliminary form, the potential for 

copper deposits in the Tucson region (the map on the 

facing page is part of one, reduced and simplified). 

Using these maps as basic data, the Board authorized 

its staff to propose an amendment to a long-standing 

county zoning ordinance to create "mineral extraction zones." The proposed ordinance provides for 

review every 5 years, so that zoning classifications can 

be changed where classification of mineral potential

Tailings (mining waste) ponds at edge of the town of Green Valley (near Tucson)

The copper mines, equally extensive and far deeper, are out of view to the left.

has changed. The preamble and selected excerpts 

from the proposed ordinance are quoted on the 

opposite page.

This proposed ordinance may not be the final 

solution, but it is a start. Experience will reveal how 

effective it is in protecting the resource from the 

expanding city. Still to be enacted (as of 1977) are

comparable measures to protect the city from 

development of the resource. (Article C of the 

proposed ordinance does forbid residential, commercial, and industrial development in "metallic 

mining residual hazardous areas" until such areas 

have been certified nonhazardous by a registered 

geologist or soils engineer.)

24
MORE THAN 1,000_FEET

,-* 

V.

XU-- Y--T "-v.

Potential for copper deposits near 

Tucson (at scale of 1:250,000)

A more potential

B intermediate potential

C less potential

....... Gradational boundary

: ':::::'-: between map units

The Tucson region contains many large 

deposits of copper minerals that have 

been commercially mined, and more are 

still to be discovered. The relative 

copper-bearing potential of the rocks 

has been appraised, based on the location and characteristics of known ore 

bodies and prospects; on the age, type, 

and alteration of rocks; on the intensity 

of rock fracturing; and on geophysical 

measurements. The relative potential for 

silver, gold, uranium, lead, and zinc is 

similar to that for copper. 

Because depth of cover may significantly 

deter ore discovery and mining, the 

map shows where the blanketing deposits are more or less than 1,000 feet 

thick. The boundaries will surely change 

as knowledge and experience accumulate. Reduced and simplified excerpt 

from Preliminary Map Showing Potential 

for Copper Deposits in the Tucson 2° 

quadrangle, Arizona OF 76-458.

Major copper deposit producing in 1974

Minor productive copper deposit

O

Copper occurrences

... a vital resource that must not be lost

ORDINANCE NUMBER

AMENDING THE PIMA COUNTY ZONING ORDINANCE NUMBER 1952-111 BY ADDING ARTICLE 44 MINERAL EXTRACTION ZONES

BE IT ORDAINED BY THE BOARD OF SUPERVISORS 

of Pima County, Arizona:

Section 1. That the Pima County Zoning 

Ordinance Number 1952 111 be amended by adding 

Article 44 Mineral Extraction Zones to read as follows:

ARTICLE 44 

MINERAL EXTRACTION ZONES

Sec. 4401 PURPOSE

The purpose of this article is to protect economic 

mineral resources and to insure the orderly and 

systematic development of these mineral resources 

while protecting the public health, safety, peace, 

comfort, convenience, and general welfare of the 

people of Pima County and to secure for them the 

social and economic advantages of an orderly efficient 

use of land and also to inform potential land owners 

of the possibility of mining in the area in the future as 

authorized by the Arizona Revised Statutes (A.R.S. 

11-806).

Sec. 4403 AREAS WHERE RESIDENTIAL DEVELOPMENT SHALL BE REGULATED

A. Active Metallic Mining Areas

B. Metallic Mineral Occurrence Areas

C. Metallic Mining Residual Hazardous Areas

D. Patented Claims and Active Metallic Mines 

within Withdrawn Areas

Sec. 4405 REVIEW

The Active Metallic Mining Area Zones and the 

Metallic Mineral Occurrence Zones will be reviewed 

no less than once every five years. Areas no longer 

designated Class A on U.S.C.S. Geology, Production 

and Mineral Occurrence Open File Maps (74-143) 

shall be considered for rezoning in accordance with 

the adopted area and neighborhood plans of Pima 

County. 

A. Active Metallic Mining Areas

a. Major Areas

Contiguous land areas 100 acres or greater in 

size owned or leased by mining companies or 

persons which contain or are utilized for 

metallic mining currently in production including but not limited to open pit mining, 

underground mining, subsidence areas, 

shops, dumps, tailings ponds, shafts, mills, 

smelters, haul roads, and all other adjacent 

and ancillary structures associated with metallic mining operations.

1. A buffer zone will extend no less than one 

mile from the perimeter of the Major 

Active Metallic Mining Area. B.

2. Residential densities shall not exceed one 

dwelling unit per thirty-six acres (1 D.U./36 

acs.) within the Major Active Metallic Mining Buffer Zone.

3. All other uses permitted by Section 801 of 

the General Rural Zone shall be permitted 

within the Major Active Metallic Mining 

Buffer Zone.

b. Minor Areas

Contiguous land areas less than 100 acres in 

size owned or leased by mining companies or 

persons, which contain or are utilized for 

metallic mining currently in production including but not limited to open pit mining, 

underground mining, subsidence areas, 

shops, dumps, tailings ponds, shafts, mills, 

smelters, haul roads, and all other ancillary 

structures associated with metallic mining 

operations.

1. A buffer zone extending no less than six 

hundred and sixty feet (660 feet) shall extend from the perimeter of all sides of the 

Minor Active Metallic Mining area.

2. No residential or commercial uses shall be 

allowed within the minor active metallic 

mining area buffer zone.

3. All other uses permitted by Section 801 of 

the General Rural Zone shall be allowed 

within the Minor Active Metallic Mining 

Area Buffer Zone.

Metallic Mineral Occurrence Areas

Metallic Mineral Occurrence Areas are defined as 

lands classified as "A" and underlain by less than 

1,000 feet alluvium on U.S.G.S. Map 1-844-G. 

"(Preliminary) Map showing potential for copper 

deposits in the eastern three-quarters of the 

Nogales 2° quadrangle, Tucson area, Arizona," 

and open-file map (76 458) "(Preliminary) Map 

showing (potential for) copper deposits in the 

Tucson 2° quadrangle, Arizona."

a. Residential development shall be restricted to 

one dwelling unit per 10 acres (1 D.U./10 acs) 

or lower densities.

b. All other uses permitted by Section 801 of the 

General Rural Zone shall be permitted within 

the Metallic Mineral Occurrence Areas.

C. Metallic Mining Residual Hazardous Areas

Metallic Mining Residual Hazardous Areas are 

defined herein as, but not limited to: Open pits, 

shafts, tunnels, tailings ponds, mining subsidence 

area, and dumps as a result of metallic mining 

activities.

1. No residential, commercial, nor industrial development with the exception of mine uses as 

defined in Section 4402, paragraph 1 of this 

Article shall be permitted on residual hazardous areas until these lands are certified nonhazardous by a geologist or soils engineer 

registered in the State of Arizona. The geologic and soils reports shall be submitted to, 

approved and certified by the Pima County 

Highway Department.

2. If applicant has shown that the residual 

hazardous area is non-hazardous and nonmineral as certified by the Pima County Highway Department, these areas shall be considered for rezoning in accordance with 

adopted areas and neighborhood plans for 

Pima County.

[D. omitted]

25
Water problems in dry country

Conserving and protecting 

the ground-water resource

The rapidly increasing population of Tucson 

requires more and more water, a commodity always 

in short supply in arid regions. Even the major streams 

here are dry more than 300 days each year, so ground 

water is the only dependable water source unless 

water is imported. Fortunately, the basin of the Santa 

Cruz River is underlain by thick deposits of sand and 

gravel in which vast volumes of water nearly 14 

cubic miles of it, equal to 1 1/2 times the total capacity 

of Lake Mead have accumulated over the centuries, 

as water from scanty rainfall and inflowing streams has 

soaked into the ground.

But the supply of ground water is not inexhaustible. 

During 1970-72, more than 186,000 acre-feet (1 acrefoot is enough water to cover one acre of ground to a 

depth of 1 foot) was withdrawn each year from the 

Tucson basin, but the average annual recharge from 

all sources was only about 126,000 acre-feet, an 

annual deficit of about 60,000 acre-feet, about oneseventh cubic mile, which is taken from the reserves 

in storage. As a result, the water level in wells is 

falling: In the 11-year period 1966-76, representative 

wells had an average total decline of 22 feet, and the 

rate of decline is accelerating. In some areas, the 

declines are as great as 10 feet per year. If this trend 

continues, Tucson will eventually run out of water; 

long before this happens, however, the cost and 

energy consumed in pumping water from increasingly greater depths will have become prohibitive 

and deteriorating water quality at greater depths will 

force a change in water-management practices. 

Further, deep dewatering of the aquifer is likely to 

cause differential subsidence of the land surface and 

development of earth cracks, which may lead to 

failure of some structures.

More than 60,000 acre-feet of 

recoverable ground water per 

square mile

From 30,000 to 60,000 acre-feet 

of recoverable ground water per 

square mile

Less than 30,000 acre-feet of 

recoverable ground water per 

square mile

(From Osterkamp, 1973b, scale 1:250,000)

Map A. Major ground-water 

resources

Map shows estimated recoverable 

water to a depth of 1,200 feet.

Map B. Depth to water in wells

Map based on measurements where 

depth to water is less than 400 feet; 

mainly inferred in areas where depth 

to water is greater than 400 feet.

Map C. Quality of ground water

Gray areas for all three maps are underlain by rocks that 

contain only small amounts of recoverable ground water

Solving the water-deficit problem will require 

careful planning based on selection of management 

alternatives that are hydrologically, economically, 

and socially acceptable. A multitude of possible 

policies and actions exists. Among the possible 

alternatives are reducing consumptive use by conservation measures; changing land use (for example, 

converting irrigated land to other uses requiring less 

water); recycling water, including advanced treatment and reuse of waste water; importing water; 

reducing the population; and augmenting recharge. 

The ramifications of the alternatives are complicated 

and only some of them involve earth-science maps in 

significant ways. In this brief chapter it seems best, 

therefore, to go no further into long-range solutions, 

which will, of course, require continuing geologic 

and hydrologic studies.

Available information provides guidance for solving pressing immediate water problems, which we 

will illustrate for a part of the Tucson region only.

26

;*f «* '

 ^LJS:^ I*

X *' f ^IT"X " ^r\

Well

Depth, in feet, to water in wells 

that principally tap consolidated rocks

(From Osterkamp, 1973a, scale 1: 250,000)
Contains more than 1,000 mg/l

Contains more than 1.4 mg/l

Contains more than 45 mg/l

Hardness 

Contains more than 150 mg/l

Criteria of water quality

Most ground water in the Tucson area meets both the mandatory and 

recommended chemical-quality limits of the drinking-water standards 

(Environmental Protection Agency, 1975). The most undesirable 

quality features are excessive amounts of dissolved solids, fluoride, 

nitrate, and hardness.

(From Osterkamp, and Laney, 

1974, scale 1 : 250,000)

Dissolved solids. Salts or minerals dissolved in the water. The recommended limit is 500 mg/l (milligrams per liter), but more mineralized water of necessity is used for public supplies in many places. In 

this area, water containing more than 1,000 mg/l generally is mixed 

with water of lower concentration to improve the quality.

Fluoride. In drinking water strengthens teeth and prevents dental 

caries in children. Excessive concentrations of fluoride, however, 

can cause mottling of teeth. The optimum concentration in the 

Tucson area is 0.7 mg/l, and concentrations of 1.4 mg/l or more

should be rejected for public use unless diluted with water of much

lower concentration. 

Nitrate. Excessive concentrations in drinking water can be fatal to

infants. The recommended limit is 45 mg/l. 

Hardness. Not a health hazard, but reduces the effectiveness of soap

and causes incrustation on pipes, utensils, and appliances; water

with less than 150 mg/l hardness generally is not objectionable for

domestic use, and harder water can be softened ordeionized before

use.

Managing existing water 

supplies

We have seen that nearly all the water used in this 

region is from wells, a few feet to many hundreds of 

feet deep, that tap saturated sand and gravel beneath 

the surface of the Tucson basin. Small amounts of 

water, usually sufficient only for a single household, 

also can be obtained from the ground in mountainous areas and along the edges of the basin. Generally, 

the depth to water in wells developing these small 

supplies is not more than a few hundred feet.

Information from many hundreds of these wells 

makes it possible to say a great deal about the 

quantity and quality of water in Tucson's underground reservoir. This information, assembled and 

summarized in the maps on these pages, provides the 

hydrologic basis for indicating areas with existing or 

potential constraints on development.

Development of the ground-water resource in the 

Tucson basin has now reached the point where 

virtually every drop of economically recoverable 

ground water is bound to be developed. These three 

maps, used together, provide part of the basis on 

which the water manager can make sound decisions 

regarding the optimum development of the groundwater resource. The most critical problems facing the 

water manager in the Tucson area are locating wells 

so as to maximize efficiency and minimize cost while 

maintaining a satisfactory quality of water in the 

supply. Thus, the optimum location of wells involves 

tradeoffs, and the maps are useful tools in evaluating 

them. For example, much water is stored directly 

below downtown Tucson itself, although some of 

it is high in dissolved solids. Excessive water-level 

declines in the area could cause subsidence and earth 

cracks, which would threaten buildings. On the other 

hand, considerable water is stored below the Santa 

Cruz River, which flows through the west side of the 

city, but its quality may be poor. And so on.

In locating and developing additional water 

supplies for the near future, social, economic, and 

legal factors must be considered, in addition to the 

hydrologic ones. And much more detailed hydrologic studies will be needed before sound final 

decisions can be made. Use of these or similar 

regional maps can nevertheless narrow the targets to 

which the remaining factors social, economic, 

legal can be directed. The net result of using 

available maps in the management process will be 

much saving of time, energy, and money.

Typical water well in Arizona

Pumping water to the land surface is 

costly, the cost depending on the 

depth to water, on the ease with 

which water flows through the aquifer to the we//, and the cost of power. 

The city of Tucson, alone, requires 

about 250 wells and 2,370 miles of 

transmission pipe to supply a population of about 400,000. An economic 

balance must be struck between the 

number and distribution of wells, and 

the size and distribution of transmission pipes. This balance is hard to 

achieve because the efficiency of a 

well decreases erratically with its age 

and with decline of water level.

Already, increased cost of energy 

combined with declining water tables 

have forced some farmers to shut 

down irrigation wells. Use for public 

supply can support higher pumping 

costs because it offers greater dollar 

return per unit volume of water.

Land surf ace-

'*« " " «*.'" .' ' ' '" 

m A ** 9 »».

" " . Water level when ' ^ .'.*.: 

 . Pump is off \. *£* .'

. . . - - »- * *- ;

 . »" .« .

 . ' . '. *

, * * * i. . 

* * *> . '

 . * a- .-; .-. ' :.*-.

 * « o * ',.

Aquifer: Water is stored between * »* . '

 . * grains and commonly is t * '* * '

 * , 26-46 percent of the total *.' *. .

, ' . volume and can be drained * , * .

0 to about 10-16 percent of t' ''

. * * the volume . o c '

 * « 

' ." *

. casing ' ."." " ' * *," " ".. ".* ..' 

* '.

. . .. ; .;.' .->' . ".-..* ; :;- V'..V? .'.' 

 'Column ' ** ,*. " / . 

"pipe .- ! .. _ ".. '.

0 __" _»Jrt)ater level when , * ^ *s

, pump Is on e * ,*

: . . . * * . o

. . . -

 ?**.' ° ."' . 

. . . '..*«* '. ' ' i

 Impeller shaft transmits '.**'. *

 power from motor ' » * '

 to Impellers . . * , '

^Pump impellers force * * 

 water up column pipe * » « ,

. ' "." '

 Well casing. Typical Installation . -

 . consists of 1/8-1/4-inch-wide saw- 

> or torch-cut slots that are 8-12 ,'

 Inches long; wire-wound screen .'

 or open-iouvered pipe are also /

 common. Ground water enters * '

11 III",» well bore through the openings ?

27
APPLICATIONS IN A MOUNTAIN FRONT ENVIRONMENT

^^ 

vFront 

 «- 3>BtaA^HHl_ ^ Range ^^^^

Urban Cotridor _^,^ f "A_ ^^r ^

Colorado

oColorado Springs

Pueblo

COLORADO
^». &

In the Boulder area

Guiding development of gravel 

deposits and of unstable ground

By. E. J. Crosby, VV. R. Hansen,

U.S. Geological Survey, and 

J. A. Pendleton, City Geologist of Boulder r

In the Colorado Springs area

m

Water for new communities

in El Paso

By R. K. Livingston, U.S. Geological Survey, and 

T.Js/1. Sundaram, Assistant Planning Director,

El Paso ount

C^olorado's Front Range Urban Corridor is an 

urbanized region of diverse topography and geology 

astride the boundary of the Rocky Mountains and the 

Great Plains. Denver is the geographic, economic, 

and cultural center of this region, but a belt of 

bustling growth extends 140 miles north to south 

along the mountains from Fort Collins to Colorado 

Springs. East to west the belt is about 40 miles wide, 

reaching onto the plains at Greeley and Aurora and 

well into the mountains west of Denver.

Because of its unusually complex physical setting, 

this urbanized mountain front region faces a host of 

geologically related land-use problems. Widely 

varied bedrock, soil, and water conditions lead to 

widely varied problems, but, as in nearly all urbanizing areas, these problems center on foundation 

characteristics, slope stability, mineral extraction 

{particularly of gravel, sand, and stone), water supply, 

and waste disposal.

Earth-science maps are being used to help solve all 

these problems in various parts of the region. This 

chapter describes how they are used in three 

situations in the Boulder area, 20 miles northwest of 

Denver, and in one near Colorado Springs, 60 miles 

south of Denver.
Boulder area

Background 

of development

The Boulder area (map opposite) was selected 

because of the wealth of information available, owing 

in large part to the early use by that city of earthscience information in land management. Boulder 

was one of the first communities in the Nation to 

develop a detailed master plan that incorporates 

geologic constraints on land development into landuse planning.

Boulder's efforts reflect concern at the State level 

with earth-science aspects of land development. For 

example, since 1972 State law (Senate Bill No. 35) has 

required large proposed land subdivisions to include 

reports on streams, lakes, topography, and vegetation; on geologic characteristics significantly affecting land use; on suitability of soil types; and adequacy 

of water supply. For another example, the State 

interest in "mineral resource areas" and "natural 

hazard areas," among several other kinds of critical 

areas, has been formally declared (House Bill No. 

1041, 1974), with provisions for designating and 

administering resource and hazard areas. For a third 

example, the State has provided (House Bill No. 1529, 

1973) for the reclamation of open-mined land, 

including the requirement that the State Geological 

Survey study the "commercial mineral deposits (sand, 

gravel, and quarry aggregate) in the populous 

counties."

Boulder was also one of the first inland cities to 

employ a full-time geologist to insure that these 

constraints and also the opportunities afforded by 

the mineral and water resources of the area are 

responded to in a professional way.

Boulder is now working toward a permit system 

that will allow proposals for land development to be 

considered on the basis of individual site characteristics and current concerns such as pollution control, 

energy supplies, and controlled-growth policy. In 

new development areas, this permit system is 

expected to supersede the more rigid existing system 

of fixed-factor zoning. In connection with this 

approach the city geologist is preparing a series of

1:12,000-scale maps (1 inch equals 1,000 feet) that 

provide much more detailed information than do the 

1:100,000-scale and 1:24,000-scale maps of Federal 

and State agencies. Proposals for development in the 

Boulder urban area are checked against all these 

maps for possible geologic hazards or other geologic 

constraints or opportunities. In turn, new data 

obtained in required site investigations are used to 

update the mapsv

Boulder, Colorado, from the air.

30
I I

 x-' " ' A*4* fci " )<' " 6T

vN j_C^ M 'i <5r N A «a* - *V"\ /y's-"^ '..

 \ j/M? /fond tWtei/ U.MXJU

" »*-lJ^«> ' ~f4-'iirt,V't' 9

io)_ ^S,,/X7S > ^j d&ff ^ ^

Lee Hill

,> v

unshine \ 

.-'- S»

 r;

NXT,ON AL ^^^^^^^c^wy^.^?^;' ;- * rw T-T -

I V ^i!*1 N^^i ; ^ ^xT' ' j/^^y^;- - WRK^^-.^*«r

^ .-'-^M^sil^P^ AS^ ^.i?B B- - *^\P3T^ sr4^^^^

/ ^^/^-^^^ f ^^^M/^H^^\.

JZ^Y^ BafalfcK ^J$K;~W \ ''' /JOAO1'

? r^n -YJrn>- -;

\x^ \ *"S ~

\ w>- ; } } J ¥- ~~a^ ''s' \H^ i^-^s,.

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«5 Y *& ^ ' \ T

' A, JUf^ATM'MIC EKERI'.Y J

T- K' ^ ^," --' I /

<7 ^fe' *^MSrt2«liiN >

Topographic map of the Boulder area

Th/s /s part of a map especially made to detail for general planning and shows

be a base for regional planning. The the entire corridor on a piece of paper

scale of 1:100,000 (1 inch on the map small enough to fit on a large conference

equals about 1 1/2 miles) offers sufficient table.

From U.S. Geological Survey, 

Front Range Urban Corridor, 

Sheet 1 and 2

5MILES

5000 5000 10,000 15,000 20,000 25,000 FEET

5 KILOMETERS

CONTOUR INTERVAL 100 FEET

31
Gravel and 

urban growth I

The Boulder area has abundant high-quality gravel 

needed to supply the increasing demands of urban 

growth and to fill the day-to-day requirements of the 

community. Gravel is a high-volume, low-unit-value 

commodity, however, and must be extracted close to 

its market to be competitive; haulage costs rise 

rapidly with distance and soon exceed the basic cost 

of the gravel itself. Also, the resource is finite, and 

some deposits are being depleted rapidly. Other 

deposits are being excluded from development by 

urban overgrowth, restrictive regulations, or adverse 

court decisions. Nearby, in the Denver area, court 

injunctions have even prevented extraction of gravel 

that had been zoned for mining for many years. 

Urban growth created the high demand for gravel, 

but some of the beneficiaries of urban growth now 

seek to curtail production.

Sequential land use

Undisturbed gravel-filled stream valley 

(lower left); producing gravel pit (upper 

left); pit filling and restoration of land 

surface (upper right); use of filled-pit 

area as a factory site (lower right). S. D. 

Schwochow, Colorado Geological 

Survey.

In looking toward the future, the City of Boulder 

and the County of Boulder must decide what shortterm and long-term measures are needed to protect 

the quality of life in their respective jurisdictions. At 

the same time, provision must be made for their 

community's constant need for gravel. Conflicts of 

interest are inevitable. For example, in an area where 

many structures have been damaged by swelling and 

shrinking with changes in water content of some soils 

or rocks, the value of a gravel deposit as a foundation 

site, without shrink and swell problems, may compete 

with its value as a source of aggregate for concrete. 

But planned sequential use of a gravel-bearing site 

may reduce or eliminate conflict (see accompanying 

diagram). Where gravel pits have been reclaimed, 

they commonly have proved more suitable for 

industrial, open-space, or recreational use than for 

residential development. Site value can be enhanced 

by good environmental design.

Maps play an important part in planning and 

decisionmaking involving gravel in the region. They 

have been compiled at scales ranging from very large 

to very small, depending on the uses to be made. To 

provide overviews for regional planning, maps 

showing the extent of gravel and related construction 

materials along the entire mountain front region have 

been prepared at the small scale of 1:100,000 (1 inch 

equals about 1.6 miles); an excerpt of these maps near 

Boulder is on the facing page.

GRAVEL DEPOSITS UNDERLYING TERRACES AND FLOOD PLAINS - 

Pebbles generally well rounded, unweathered; deposits contain little deleterious "lime" (CaCO3 ). Lithologjc composition reflects bedrock in 

source areas along Boulder Creek, St. Vrain Creek, Lefthand Creek, the 

Little and Big Thompson Rivers, and the Cache La Poudre River; clasts 

are composed chiefly of quartzite, granite, gneiss, and pegmatite. Few 

or no reactive constituents. Source of best quality gravel for concrete 

aggregate and road metal

UPLAND GRAVEL DEPOSITS UNDERLYING PEDIMENTS AND HIGHLEVEL TERTIARY SURFACES - Poorly stratified and poorly sorted 

cobble and boulder gravels near mountains. Average size of stones decreases away from mountains. Thick well-developed old soil profiles 

contain much clayey material and thick deleterious caliche (CaCO3 ) 

zones as cement and rinds on stones. Low-quality source of concrete 

aggregate; source of road metal

FINE-GRAINED IGNEOUS ROCKS - Crop out adjacent to the mountains 

as dikes and sills. The Valmont dike of shoshonite (alkalic basalt) has 

been quarried in the past. A sill of rhyodacite 3 miles (4.8 km) southwest 

of Lyons is quarried for crushed rock

COARSE-GRAINED IGNEOUS ROCKS - The Boulder Creek Granodiorite 

and the Silver Plume Granite, quartz monzonite, and quartz diorite (tonalite) occur along the west edge of the area, most of these rocks are south 

of Pinewood Lake. Tonalite or quartz diorite occurs as scattered long 

narrow bodies north of Pinewood Lake. Many small bodies of pegmatite 

are along the northwest edge of the area. Most of these rocks are potential 

sources of high-quality crushed-rock aggregate, although pegmatite may be 

unsuitable

METAMORPHIC ROCKS - Much of the area of crystalline rocks north of 

Pinewood Lake is underlain by micaceous metamorphic rocks. Quartz 

mica schist, various kinds of gneiss, and amphibolite are the common rocks. 

Foliated rocks are inferior to nonfoliated granitic rocks, but many gneisses 

have been used for aggregate elsewhere

QUARTZITE - The quartzite of Coal Creek near the mouth of Coal 

Creek Canyon between Golden and Boulder is a white, gray, red, 

and black fine- to coarse-grained well-bedded quartzite that is a 

potential source of high-quality crushed-rock aggregate 

SHEAR ZONE - Crushed, broken, or sheared rock along a major fault; much 

altered locally. Undesirable as a source of crushed rock for concrete aggregate, but might be used locally for road metal or fill

X

02-68-03 a

City and tilt

BOUNDARY OF DEPOSIT OR LINE OF CONTACT BETWEEN DEPOSITS

LARGE GRAVEL PIT 

GRAVEL PIT

DISTRIBUTION OF GRAIN SIZES IN GRAVEL DEPOSIT, IN PERCENT 

BY WEIGHT - Diagram indicates analysis of a sample that contained 

15-percent clay and silt, 35-percent sand, 30-percent granules and pebbles, 

and 20-percent cobbles and boulders. Number adjacent to diagram is 

land-net location: first number is township, second is range, third is 

section, and letters are sectional subdivisions. Numerical data are found 

in accompanying table

37 qm 

24 pen 

17n 

12 gn

9gr

leg

PERCENTAGE OF STONE TYPES IN DEPOSIT 

100 pebbles

a Aphanite (any dark-colored

very fine grained rock) 

ba Basalt (includes gabbro,

dolerite)

br Breccia (siliceous) 

ca Caliche 

eg Conglomerate 

cone Concretion (mostly siderite) 

di Diorite 

gn Gneiss 

gr Granite 

Is Limestone

 Based on one count of

peg

pet wd

por

qtz

qtzt

rhy

sch

sh

si

ss

sy

u

Pegmatite

Petrified wood

Porphyry

Quartz

Quartzite

Rhyolite

Schist

Shale

Siderite

Sandstone

Syenite

Unknown

td2 

gv>6

30,

ABBREVIATED LOG OF DEPOSIT - From well records and other drilling 

or test data of U.S. Geological Survey and Colorado Division of Highways. 

Thicknesses shown are in feet

cl 

gv

Clay 

Gravel

sd 

sh

Sand 

Shale

Sandstone 

Silt

THICKNESS OF GRAVEL DEPOSIT - In feet

32
Gravel and aggregate resources near Boulder

From Colton and Fitch (1974) 

and Trimble and Fitch (1974)

5000

SCALE 1:100000

1 2 3 SMILES

5000 10,000 15.000 20,000 25,000 FEET

,5 KILOMETERS

33
Gravel and 

urban growth II

Serving the local needs requires more detailed 

maps than the regional one on the preceding page. 

Such maps, useful for general county or city planning, 

have been compiled, by the Colorado Geological 

Survey, at the larger scale of 1:24,000 (1 inch equals 

2,000 feet). Part of one of these appears to the right. 

It shows an area of high-quality gravel, in yellow, in 

a low terrace of South Boulder Creek. This gravel 

was deposited by South Boulder Creek during waning 

stages of the Ice Age, when the creek was swollen 

by meltwater from glaciers in the nearby mountains. 

Older, lower quality deposits are shown in red. A 

three-dimensional view, looking north, down the 

creek valley, is shown below.

Bird's eye view of gravel deposits

Low terrace gravel, high quality

High terrace gravel, lower quality

Gravel deposits in the 

South Boulder Creek area

From Schwochow and others (1974)

The sand and gravel map prepared for planning 

purposes is displayed on the facing page. This map 

inventories the historical production of sand and 

gravel, active extraction sites, deposits precluded 

from development, and the quality and extent of the 

available unextracted resources. It is based on one of 

a series of maps at twice this scale 1:12,000 (1 inch 

equals 1,000 feet) that has been prepared by the city 

geologist, for use in site decisions and in compliance 

with a 1973 State law that requires a master plan for 

sand and gravel extraction in urban areas.

The City of Boulder in 1976 authorized a 20-year 

plan to extract gravel from a 440-acre tract along

1000

SCALE 1:24000 

o

1000 2000

 l

3000

l 

4000 5000

l 

6000

 l

7000 FEET

1 KILOMETER

CONTOUR INTERVAL 10 FEET

South Boulder Creek. This plan calls for concurrent 

step-by-step reclamation of the tract as open space 

with an artificial lake as a long-term objective.

Private citizen groups that oppose gravel mining in 

this area, however, contend that South Boulder valley 

is scenic open space at a major approach to the city

and should be retained in its present pastoral form as 

a part of Boulder's green belt. To mine or not to mine 

the gravel, therefore, is a complex controversial 

question that probably will be decided ultimately in 

the courts, or by ballot on a referred vote of the 

citizens of Boulder. The physical exploration of the

34
Extraction precluded by development

Site of previous extraction

Current extraction permit

Owned open space

Potentially first-class sand and gravel deposit

Potentially extractable lower class sand and 

gravel deposit

Sand and gravel planning map for part of 

the Boulder urban area

From J. A. Pendleton, city geologist. Boulder, Colorado (mapping scale 1:12,000)

*

1000 0

1

SCALE 1:24000

0

1000 2000 3000 4000 5000

5 0

1

6000 7000 FEET

1 KILOMETER

1 MILE

CONTOUR INTERVAL 10 FEET

deposit, its quality, and its delineation on maps are 

largely geologic matters, but the ultimate land use will 

be decided mainly on legal, socioeconomic, environmental, and political grounds.

When mineral resources are involved in land-use 

decisions, the first step should be to determine the

general extent and quality of the resource, in this 

instance from the gravel maps, and the relation of the 

resource to urban growth patterns and long-term 

projected land uses, as determined by urban 

planners. Colorado law, since July 1, 1973, forbids 

land uses in populous parts of the State that would

interfere with present or future extraction of 

commercial-grade sand and gravel deposits. Compatible preextraction uses would include agriculture, 

athletic fields, parking lots, open space, and green 

belts, among others. The law also requires reclamation plans before the resource is mined. The law is 

not retroactive and does not apply to lands previously 

zoned for other uses but does provide a legal basis for 

communities such as Boulder to plan realistically for 

the conservation and orderly use of their exploitable 

mineral resources in ways that are compatible with 

long-range community objectives.

35
Land that swells, 

shrinks, and slides I

Volume changes from wetting and drying of clays 

cause extensive damage to buildings, pavements and 

poured concrete slabs (sidewalks, patios, basement 

floors, highways, and landing strips), buried utility 

and service lines, and ground surfaces. The plains 

region east of the Rocky Mountains, within which 

Boulder lies, has some of the highest potential for 

shrink-swell damage in the country. Typical damage 

in Boulder from shrinking and swelling clays is 

illustrated in the accompanying photographs. The 

potential of soil and bedrock near Boulder for 

swelling with changes in moisture content is shown 

in the map opposite. Where this potential exists, a 

corresponding potential for slope instability and 

resultant landslides is also present.

Wall damage caused by shrinking and 

swelling clay below foundation of 

house. Photographs by ]. A. Pendleton.

NOTE: The swell potential categories ehown below 

generally apply to the upper 10 ft of soil or 

rock. However, local variations in thickness of 

surficial deposits should be expected. Therefore, 

this information should not be considered adequate for an individual building site. A registered professional soil engineer should be 

utilized for site investigation and foundation 

design for every building site in the Front 

Range Urban Corridor.

VERY HIGH SWELL POTENTIAL: This category includes only bedrock or.weathered bedrock.

precautions listed below under "high swell potential" must be utilized. Although construction

in these areas is often unavoidable, alternate

non-construction uses might be considered for

This category generally includes only bedrock, weathered bedrock,and colluviwn

Careful site investigation, special foundation deand proper post-construction landscaping and

maintenance are required to prevent or minimize

This category includes

several bedrock formations and a few surficial

deposits of variable thickness. Special foundation designs are generally ncessary to prevent

LOW SWELL POTENTIAL: This category includes several

bedrock formations and many surficial deposits.

thickness of the surficial deposits may be variable.

therefore, bedrock <with a higher swell potential

may locally be less than 10 ft below the surface.

WINDBLOWN SAND OR SILT: Although this material 

generally has low swell potential, the upper 6 

inches to 12 inches may locally have moderate 

swell potential. Windblown material may be 

subject to severe settlement or hydrocompaction 

when water is allowed to saturate the deposits. 

The thickness of windblown material may be very 

variable, therefore, bedrock with higher swell 

potential may locally be less than 10 ft below 

the surface.

Slumps caused by expansive clay are 

common along highways in the Boulder 

area. Only a nuisance when small 

(above), they can lead to large-scale 

failure of the roadway itself resulting 

in major damage (below).

36
TANDLEY LAKK

5506 uerai

lart (1974)

Potentially swelling soil and rock in the Boulder area

5000

SCALE 1:100000

1 2 3 SMILES

5000 10,000 15,000 20,000 25,000 FEET

5 KILOMETERS

CONTOUR INTERVAL 100 FEET

37
Land that swells, 

shrinks, and slides II

Application of swell-potential information to landuse management is well illustrated by the small but 

representative proposed Dakota Ridge residential 

development, at the west edge of Boulder. Zones of 

potential swelling ground and unstable slopes in the 

vicinity of the proposed development are shown in 

the two maps, right. These maps were used by the 

city geologist, by the Planning Department and City 

Council of Boulder, and by property owners seeking 

approval of the proposed development.

In 1972, a proposal for city annexation of 0.67 acre 

(upper plot plan, opposite) of the tract and for 

construction of a single residence under existing 

"rural- residential" zoning was refused because of 

citizen opposition and for geological and technical 

reasons. A second developer applied for annexation 

and rezoning in 1974. Citizen opposition again 

defeated the proposal. The developer then increased 

the size of the parcel to 1.11 acres.

Examination of the site by the city geologist disclosed several potentially detrimental factors: (1) The 

tract was on steeply dipping clay rock, called the 

Pierre Shale, with an average surface grade of 20 

percent. Grades greater than 10 percent in Pierre 

Shale have been susceptible to failure throughout the 

Boulder urban area, particularly if the rock is wet. The 

results of debris and landslide movement on steep 

slopes in Pierre Shale within Boulder are shown in the 

photographs on the opposite page. (2) The Pierre 

Shale under the site has a moderate to severe 

shrink-swell potential. (3) An irrigation ditch, which 

crosses the tract, leaks in several places and could 

saturate the rocks forming the slope proposed for 

development. (4) A distinct swale crosses the 

northern half of the tract from northwest to 

southeast. Slope runoff concentrates in this swale, as 

evidenced by dense vegetation.

The detrimental factors affecting the tract were 

clearly interrelated, and development would require 

careful planning to avoid damage to structures. 

Leakage from the irrigation ditch could cause slope 

failure. In addition, seasonal shrinking and swelling of 

the ground might damage any structure. Construction on the site could also drastically alter the existing 

drainage pattern, possibly increasing the potential for 

slope failure,foundation damage,and flooding during 

severe storms.

Potentially unstable slopes in part of Boulder

LSK, known landslide deposits; LSHP, 

area of relatively high potential for 

landslides, due to leakage from upslope irrigation ditches; LSP, area of 

potential for landslides; LSL, area of 

low potential for landslides.

Potentially swelling ground in part of Boulder

NSP, area of no swell potential; MSP, 

area of moderate swell potential; 

Z.SP, area of low swell potential; CSP, 

area of potentially swelling ground 

covered by more than 5 feet of nonswelling surficial material.

From Map by J. A. Pendleton 

Publication scale 1:24,000 

mapping scale 1 :1 2,000

From Map by J. A. Pendleton 

Publication scale 1:24,000 

mapping scale 1 :12,000

O-esidentrai" 

development

38
'$%&%&%& SSSs£&s'/SZZ£srS?+

Proposed Dakota Ridge development 

project in Boulder

Shown are original 1875 subdivision plot, 

area proposed for development in 1972, 

and additional area proposed in 1974.

roftssT Avnwe

Proposed Dakota Ridge planned 

residential development, 

as submitted in 1974

Proposed Dakota Ridge subdivision, 

as approved by Boulder 

City Council in 1975

In June 1974, having realized how costly it would be 

to develop this site, the developer abandoned the 

single-unit concept and applied for annexation, 

rezoning, and approval of a seven-unit planned residential development (middle plot plan at left). This 

proposal was rejected by the Boulder Planning Board, 

but the City Council granted annexation and 

deferred rezoning, unofficially denying the sevenunit density on the basis of geological conditions and 

lack of applicant information.

In September 1974, the Planning Board recommended that the parcel be zoned "low density 

residential established" (minimum lot size 7,000 

square feet), without "planned residential development" approval, in order to retain the basic nature of 

the neighborhood. The owner next submitted a fiveunit subdivision plan (lower plot plan at left), 

including engineering reports on the geological 

complications. The report (1) confirmed the shrinkswell potential of the ground; (2) stated that "seepage 

from the Silver Lake Ditch is so severe that this source 

of ground water must be eliminated to allow 

development of the property" and recommended 

replacing the open ditch with a leak-proof culvert; (3) 

recommended a drainage swale above the culvert to 

divert runoff into the existing ditch; (4) stated that 

roadway pavement construction would require 

chemical stabilization of the subbase and a flexible 

pavement, 12-inches thick; (5) recommended peripheral drains and drilled pier and grade-beam 

foundation construction.

The consultants' report was accepted by the city 

geologist, and in May 1975 the City Council approved 

the subdivision with the condition that all of the 

consultants' design recommendations be implemented to the satisfaction of the City Building 

Department. The owner also had to obtain variances, 

granted in January 1976, for lot size, height limitations, parking requirements, and open-space requirements. Permits for the construction of the five 

approved residences were to be granted when 

complete site analysis, soil testing, foundation 

designs, and grading plans were all approved.

It was a long and expensive procedure, but it 

provided greater protection to future residents and to 

adjacent established homes. Also, as it turned out, the 

procedure resulted in greater profit to the developer. 

It would have been much shorter and less costly if the 

development had been carefully planned from the 

beginning.

Scale all maps 1:120O reduced from original scale of 1:600

A 7-ton fragment of a 35-ton rock-fall boulder lodged 

in the patio of a foothills subdivision home on the 

west edge of Boulder. Photograph by ]. A. Pendleton.

Failure on a steep Pierre Shale slope in Boulder. 

Photograph by J. A. Pendleton.

39
Subsiding land

Underground coal mining was an important 

industry in the Boulder area from 1863 until the 1940's, 

and a few small mines still operate. Openings from 

mined coal are within a few hundred feet of the 

surface over large areas. The ground over mined coal 

beds is prone to subside in some places gradually 

but in others suddenly and without warning 

months, years, or decades after the coal has been 

removed. Fires in abandoned mines have created 

additional risk and have extended the area of 

potential subsidence. This subsidence is a potential 

hazard that should be weighed carefully before landuse changes are made.

Mined areas in part of the Boulder-Weld coal field 

are shown on the map below. Most of the area is rural, 

with a few small former mining towns and rural trade 

centers. The area, however, is in the path of urbanization spreading eastward from Boulder and northward from Denver, and sizable subdivisions have 

already been contemplated. The map also shows the 

many faults which break the country up into long, 

irregular blocks and greatly complicate both mining 

of the coal and management of the potentially 

subsiding land.

Subsidence and collapse of ground surface above old coal workings and mine fires about onequarter mile east of Marshall. Photograph by R. B. Cotton and R. D. Miller, U.S. Geological Survey.

Mined areas of part of the Boulder-Weld coal field

^.Tl> /\ \- . , 

x^V-vCc i TTK ) -J

i %VA v ^1*^

eSTn^ 7^V, , > '% ^r^

Mined area

Shaft 

(location approximate)

Fault Dashed where approximately 

located; U, upthrown side; D, 

downthrown side. Shown at levels 

of coal beds; most fault planes dip 

70°- 80° NW. and therefore may 

intersect the surface east of position 

shown on map

3 MILES _i

I

4 KILOMETERS

From Colton and Lowrie (1973)

40
Subsidence and collapse of ground surface above old coal workings and mine fires at east edge 

of Marshall. Photograph by R. B. Co/ton and R. D. Miller, U.S. Geological Survey.

A subsidence-potential map has been made by 

combining the mined-area map with mapping of 

surface expression of subsidence or other instability, 

information on the depth of mine workings and distribution of remaining coal, the location of burning 

areas, and the characteristics of faults. A part of this 

map near Marshall, a former coal-mining center, 

is reproduced enlarged below. This map, constantly 

updated by information from the Colorado Geological Survey, the city geologist of Boulder, and 

private engineering firms, has provided a basis for 

zoning decisions in Boulder County, including rejection of some development proposals.

The nature and scale of subsidence above old 

coal mines is dramatically shown in the photographs. The scenes are from near Marshall, where 

much of the coal was within 50 to 150 feet of the 

surface. Here subsidence has led to actual collapse of 

ground above old shallow workings, some of them 

burned. Even the room-and-pillar pattern of the mine 

is evident at the surface. The effect has been 

devastating.

If the coal were being removed today, strip mining 

might be employed instead of underground methods. Much more coal could be recovered, and the 

land surface would be much more amenable to 

reclamation and, therefore, to safe and practical use 

after mining. But strip mining brings its own 

environmental problems, and underground mining 

might be more desirable in some situations.

Areas of potential subsidence over coal field near Marshall

SMF, mine fire area with extreme subsidence risk 

SPU, previously undermined subsidence-risk area

SFU, area underlain by subbituminous coal which 

may be subject to subsidence if mining 

occurs in the future

1 KILOMETER

From a map of a larger area 

by J. A. Pendleton. Scale 1 

mapping scale 1:12,000

24,000

^rr--j o. 11 \ I

eXXJ' 5: I

41
I I

Colorado Springs 

____area____

Background of 

water needs in 

El Paso County

El Paso County, together with Colorado Springs, its 

largest municipality, is one of the Nation's fastest 

growing urban areas. From 1950 to 1970, the 

population of the county more than tripled from 

about 74,500 to 245,000. The population by the year 

2000 would range from about 360,000 to 800,000, 

according to alternate projections for slow to rapid 

growth. The El Paso County Land Use Department is 

using a "moderate" growth curve, which anticipates a 

population of about 550,000 by the year 2000, as the 

basis for its planning program. The current level of 

growth is straining the area's energy and water 

resources. In 1973, as a result of a shortage of natural 

gas for heating, a temporary moratorium was 

declared on new construction within the metropolitan area of Colorado Springs. This sudden brake 

on the region's population and economic growth 

caused great concern among the entire community 

and resulted in an increased interest in natural 

resource appraisals. One of the more serious 

concerns in this semiarid region is the problem of 

water supply.

Knowledge of the availability and quality of water is 

vital to planning for the future of this growing region. 

Local government and civic groups have increasingly 

felt the need for a thorough water study, particularly 

in view of recent State laws which require all 

developers of subdivisions to show that an adequate 

water supply will be available and to submit a report 

to the county indicating the quantity, quality, and 

dependability of this supply. In 1972, the U.S.

1000

1950 1960 1970 1980 1990 2000

Historical (1940-74) and projected (1975-2000) population of

El Paso County

Geological Survey began a comprehensive 3-year 

study of ground water and surface water in the county 

in cooperation with the county, the city of Colorado 

Springs, the Pikes Peak Area Council of Governments, 

and the U.S. Air Force Academy.

The principal objectives of this study were to 

determine the availability and quality of ground 

water; to document current ground-water development, annual ground-water withdrawal, and the 

effects of current development; to determine the 

quality of surface waters; to estimate mean annual 

and peak flows of the principal streams; and to

develop the ability to predict future development 

alternatives by means of a ground-water computer 

model. Let us examine how this model is being used 

to determine the effects of increased pumping on 

water levels in the Dawson aquifer, the main source of 

undeveloped ground water in El Paso County, and is 

thus helping planners and managers to evaluate the 

impact of new subdivisions and developments. To do 

so, we will first describe the county's general water 

resources, then describe the Dawson aquifer, and 

conclude by discussing the ground-water model and 

its uses.

Colorado Springs, a rapidly growing Front Range community at the foot of Pikes Peak.

42
Base from U.S. Geological Survey 

State base map, 1969

10I15 MILES 

1

10 15 KILOMETRES

Water resources of 

El Paso County

Precipitation, the primary source of water in El Paso 

County, increases with altitude within the county: 

Mean annual precipitation ranges from less than 12 

inches at an altitude of 5,300 feet in the southeastern 

corner to more than 30 inches at 14,000 feet near Pikes 

Peak. Most of the county is in the semiarid plains 

region which lies east of the mountain front, where 

annual precipitation is only 12-16 inches. Throughout 

the county about 20 percent of the precipitation 

occurs as snow.

Runoff similarly increases with altitude. The 

mountain region contains many perennial streams 

with fairly abundant surface water, whereas most of 

the streams in the plains region flow only intermittently. About 95 percent of the county is drained by 

generally south- and east-flowing tributaries of the 

Arkansas River, including Fountain Creek, Chico 

Creek, and Big Sandy Creek. The rest is drained by 

north-flowing tributaries of the South Platte River.

Most of the water development in the county has 

resulted from the needs of Colorado Springs. The 

Colorado Springs water supply, aggregating about 45 

million gallons per day in 1974, comes from many 

sources and reflects, in a general way, total water 

development in the county. About 40 percent of the 

supply comes from streams within the county, and 

only about 9 percent from ground-water sources. The 

rest is imported.

The surface waters in El Paso County have been 

extensively developed and are generally overappropriated. For the foreseeable future, the Colorado Springs water supply cannot be expanded much 

beyond its existing service area because the supply is 

severely limited by water rights and other restrictions. 

Therefore, the rapidly growing suburban areas and 

planned land developments in the county will have to 

depend on local sources, mostly ground water, for 

their water supply. A few small thin alluvial aquifers 

are present, but for most of the developing area the 

Dawson aquifer will be the principal source of water.

Location and stream system of El Paso County

X c WL- f ^ f ^^-

- ""* -- *£'' ^y^:''*lfay>f"^-^>f .}f"^^ff^'^s~'*'~.s'

,. V < . T\\V" 'tfcSV1- "- A!^^»- ^<K^:^--

v.V' J: M' " \.^xi V*-

T ' v '<V it \ «'. ". >^$#" ^

v * y ' < *^L ^f\*C" «A /

"PrecambriaivN< I \ - "^s-.*».".

Not to scale

The hydrologic cycle in El Paso County

43
The Dawson aquifer 

in El Paso County

The Dawson aquifer, which coincides with the 

Dawson Formation, underlies about 850 square miles 

in northern and central El Paso County and contains 

an estimated 97 million acre-feet of ground water in 

storage. The water bearing Dawson Formation, 

shown on the diagrams at upper right, is a great lensshaped body of sandstone that is variably cemented;

MT

BLODGETT 

PEAK

 " ^

Not to scale

Location of geologic sketches in El Paso County

105° 00' 104-30

it includes a few beds of shale. Only the southern part 

of the sand lens is in El Paso County, where it is about 

2,500 feet thick near Black Forest. The lens thins to 

zero within 10 miles westward at the mountain front, 

within about 10 miles southward beneath the city of 

Colorado Springs, and within about 30 miles eastward; its capacity to store water, of course, diminishes 

correspondingly.

Ground-water withdrawal from the Dawson aquifer is now (1977) relatively small, about 5,000 acre-feet 

annually. Water is withdrawn for municipal use from 

20 to 30 large-capacity wells and for domestic use 

from several hundred small-capacity wells. The 

average well depth is about 330 feet and reported well 

yields range from 5 to 400 gallons per minute.

Water levels in the Dawson 

aquifer

Water levels in the Dawson aquifer (map, middle 

right) range from 6,400 to 7,500 feet above mean sea 

level. The average depth to water is about 100 feet. 

Ground-water movement, as shown by arrows on the 

water-level map, is from higher to lower altitudes and 

generally is perpendicular to the water-level contours. The ground water is therefore flowing away 

from the Black Forest area, where the water-level 

altitude is highest.

The water levels in wells in the Dawson aquifer have 

not changed much in recent years, indicating that 

natural recharge from rain and melted snow (map, 

lower right) about equals natural discharge to streams 

and adjacent rock formations. The trend of the waterlevel contours shows that a large part of the natural 

discharge of grou nd water from the Dawson aquifer is 

to Monument Creek. Seven surface-water gain-andloss investigations in 1973 and 1974 found that an 

average of about 7.5 cubic feet per second of the 

streamflow in upper Monument Creek was flow from 

ground water to the stream. This measured gain 

represented about 30 percent of the average flow at 

the end of this reach during these investigations.

39°00'

Approximate li 

Dawson aquifer V

Water level altitudes in the Dawson aquifer

Contours, at 100-foot intervals, show indicate direction of ground-water 

water levels as of spring 1974. Arrows movement.

105-00' 104-30'

\ Ellicott N y

/ Rush""^1-.

:-S-- / . .

' 'V

15 KILOMETERS

RECHARGE, IN INCHES PER YEAR, 

ESTIMATED BY DIGITAL MODEL

Natural recharge to the Dawson aquifer

Less than 0.05 

0.05 to 0.5 

0.5 to 1.0

1.0 to 1.5

1.5 to 2.0

2.0 to 2.2

44
Slocum and - -r-m» 

Piney Creek'^^ ''^l''^'*'/,',^,.'.'. Verdos Alluvium^ -

alluvium ^TT ^>T>'-'r-z - -*-" *'; gSga<tt^^8^

Dawson Formation N Water ta

Rocks of northern El Paso County 

in three dimensions

The edges of the blocks are located on 

the small map, far left. The Dawson 

Formation, a thick body of water-bearing 

sandstone near the surface, is the only 

undeveloped large water source in El 

Paso County.

Mathematical model of the 

Dawson aquifer and its uses

If we know enough about the way hydrologic 

systems in general work, and about how the Dawson 

aquifer in particular has worked in the past, we should 

be able to predict how this aquifer system is likely to 

respond to future changes. Changes may occur either 

by gains or losses of water, both of which, in the short 

term, are more likely to be due to man's activities than 

to natural events. To make such predictions, however, is difficult, involving as it does not only the 

physical dimensions and water-bearing properties of 

the aquifer but also the amount of ground water in 

storage, the rate and direction of ground-water 

movement, natural recharge, and discharge by 

evapotranspiration, flow to surface waters or other 

aquifers, or withdrawal by wells.

Complicated hydrologic systems can be simulated 

by mathematical models. Digital computers can then 

be used to evaluate simultaneously all the factors that 

influence the systems in a fraction of the time it would 

take to perform all the calculations by hand. Such a 

model has been made for the Dawson aquifer and is 

being used to assist in making decisions about water. 

The model, for all the power of the computer, is an 

imperfect simulation of a complex natural system 

whose characteristics are incompletely known. Predictions made by manipulating the model are 

therefore only approximations, to be used with due 

caution.

Basic to all decisions involving the Dawson aquifer 

are the distribution and rate of natural recharge, for 

withdrawal of water at a greater rate for very long 

times will inevitably lead to decline of the water level, 

increasing the difficulty and cost of pumping and 

eventually exhausting the supply. Modeling shows 

that the natural recharge rate is about 2.0 inches per 

year in the vicinity of Black Forest and decreases with 

decreasing altitude to less than about 0.05 inch per 

year near Ellicott and Ramah. This is shown on the 

natural recharge map just referred to.

To use the hydrologic model for prediction several 

assumptions must be made. It is assumed that (1) all 

persons living in an area underlain by the Dawson 

aquifer and not zoned by the city of Colorado Springs 

would be supplied by wells tapping the Dawson and 

within 2 miles of the house, (2) per-capita use of water 

would be about 170 gallons a day, (3) population 

would increase in equal increments of 28,530 persons 

every year, representing 5-year withdrawal increments of 4.85 million gallons per day, and (4) 25 

percent of withdrawn water would be returned to the 

aquifer. These assumptions are based on the 

projections of local planners.

105°00' 

I I Palmei

104-30'

- -^ /. -I

 /cr^N

PREDICTED DECLINE, IN FEET 

50 to 75

Predicted water-level decline, 1975 to 2000, 

in the Dawson aquifer

25 to 50 75 to 92

Developments planned 

or under construction

Given the known rate of recharge and projected 

water withdrawals, what will be the effect pji water 

levels in the Dawson aquifer? The model pre^fct^that 

by the year 2000, the water level will decline njiore 

than 75 feet in 4 areas and as much as 92 feet in Qrte of 

these areas, as shown on the map just above. Waterlevel declines of 50-75 feet are predicted for housing 

developments now underway at Chapel Hills, 

Cimmarron, and Woodmoor, and a maximum 

decline of 92 feet is predicted at the large newly 

proposed development to be called Latigo, northeast 

of Falcon. The Latigo proposal visualizes an ultimate 

population of 55,000 persons on about 9,000 acres, all 

to be served by water from the Dawson aquifer. The 

future of this proposal may well hinge on its impact on 

the aquifer as predicted by use of the hydrologic 

model.

The model also predicts a decrease in the flow of 

Monument Creek as a result of increasing withdrawals from the aquifer. By 2000, streamflow can be 

expected to be reduced by about 2.1 cubic feet per 

second or 1.36 million gallons per day. Such a

depletion would probably affect downstream surface-water rights, and State law might require 

developers to augment the flow of Monument Creek. 

This might be accomplished by limiting the size of the 

development to avoid or reduce streamflow depletion, by recycling sewage effluent and returning it to 

the stream, by artificial recharge, or by some 

combination of these. The hydrologic model will no 

doubt influence selection of the course to be 

followed.

The model will be used extensively in evaluating all 

new proposed subdivisions in the unincorporated 

areas of El Paso County where the main source of 

water supply is ground water. With it, planners will be 

able to calculate, within the limits of accuracy of the 

model, how much water can be withdrawn from the 

Dawson aquifer in a given area, how this would affect 

water levels, and thus ultimately how much this withdrawal would affect water supply in surrounding 

areas. As more and better information becomes 

available, the accuracy, and therefore the usefulness, 

of the model will increase.

45
^^H APPLICATIONS IN A NEW ENGLAND ENVIRONMENT ^^M

Connecticut River Valley,

Connecticut

East Granby-A plan of development

for a rural community

By William H. Langer, U.S. Geological Survey, and 

Lawrence H. Johnson, Connecticut Department of

Community Affairs

* * *

¥» «* VV *£^ ' **

A W *

f

\

East Granby''

Hartford I

Waterbury i

Bridgeport

^^^^H ^^^^^^H_a H M ^^^H H^^^^^^^H^^KH 

_ - ^^B IBWIffmff^f H ^ I . ^^ l^^^^^^T^

__ drainage-area maps in__

evaluating waste-disposal conditions;

assessing impact of highway salting,

and designing bridges and culverts

By Robert L. Melvin, U.S. Geological Survey

46
East Granby

Background of 

development

The problems of East Granby, Connecticut, as a 

rural community are somewhat different from those 

of large urban areas. Sewer service extends to only a 

small part of the town, and municipal water service 

does not exist. Therefore, most of the houses rely 

upon onsite septic systems for waste disposal and 

upon onsite wells for water supply. A properly functioning waste disposal system and a safe, reliable 

water supply, both on the same property, require 

careful planning. With urban population growth demanding land, rural areas are under pressure. Urban 

development strongly competes with farming and 

also spreads into sensitive areas where it may have 

harmful effects on the natural environment. Rural 

town planning must carefully consider these special 

problems, as well as those that are common to both 

rural and urban areas.

Therefore, a somewhat different approach to 

planning may be taken in East Granby from that 

used in large urban areas. Here, large areas of land 

are available for growth, so it is easier to plan around 

natural constraints, rather than engineer through 

them. Development can be located in areas of minimum constraints, or development can be at a density 

that is low enough to minimize environmental 

impact. Of course, a sound plan of development 

for a rural community, like that for a city, should 

determine how development can be adjusted to the 

natural environment and should also determine how 

the environment can be used most effectively by 

the community.

Connecticut is one of the States that officially 

recognizes natural factors in the community planning 

process and encourages the development and use of 

earth-science information. Further, the State possesses a wealth of natural-resources data. The U.S. 

Geological Survey has had cooperative programs in 

geology and hydrology with the State for more than 

20 years. From 1971 to 1976 the Survey also funded and 

staffed the Connecticut Valley Urban Area Project, 

which was headquartered in Middletown, Connecticut. In this pilot project, geologic and hydrologic 

maps were prepared in a format designed for landuse planners and decisionmakers in central Connecticut as well as in parts of Massachusetts, New 

Hampshire, and Vermont. The Soil Conservation 

Service is also active in Connecticut and has been 

preparing detailed soils surveys for many years.

In addition, in 1969, several geologists, hydrologists, soil scientists, and planners from State and 

Federal agencies formed an ad hoc group known as 

the "Geology-Soil Task Force" which prepared a 

report titled "Use of Natural Resource Data in Land 

and Water Planning." A few years later, the State 

Department of Environmental Protection jointly 

sponsored a series of workshops with the Cooperative Extension Service of the University of Connecticut. These workshops, held at various locations 

throughout the State with representatives from every 

town in Connecticut, pointed out the importance and 

demonstrated the use of natural resource data in the 

planning process.

Shortly after these workshops were held, the town 

of East Granby revised its existing plan of development. The new plan included consideration of the 

natural environment, and as a result the town now has 

a plan of development that not only accounts for the 

projected growth of the community, but also protects 

and utilizes the surrounding environment in the 

interest of the community.

Setting of 

East Granby

The town of East Granby is a rural, residential New 

England community about 15 miles north of Hartford, 

Connecticut. East Granby is adjacent to Bradley International Airport and is easily reached by state and 

interstate highways. The town has an area of 17.4 

square miles, with less than 25 percent of the land 

being developed. There are extensive areas of 

woodland, pasture, and farmland, and in spite of the 

more obvious evidences of development, many 

sections of town retain their rural character.

Since 1970, some 250 units of multifamily housing 

and 170 single-family houses have been built in East 

Granby. An estimated 870 more housing units 

probably will be constructed by 1990. A new town hall 

was recently built in the town center, which also has a 

small business nucleus. East Granby experienced a 45 

percent increase in population from 1960 to 1970, and 

between 1970 and 1974 the population increased by 

nearly 1,000 people to approximately 4,500 residents. 

By 1990 the population of East Granby may be more 

than 7,500.

The land in East Granby is for the most part level to 

gently sloping, with the exception of the Talcott 

Mountain Ridge, which divides the town from north 

to south and consists of thick layers of ancient basalt 

lava flows. Rock is at the surface in many places on the 

ridge, and the soil is seldom more than a few feet 

thick. The presence of the ridge has dictated the 

existing road network and has directed development 

to the valleys to the east and west. These valleys are 

filled with thick glacial deposits of sand, gravel, silt, 

clay, and till, so that the underlying sedimentary bedrock is almost entirely covered.

Planning activities

East Granby established a zoning commission in 

1941 and changed this to a combined planning and 

zoning commission in 1953. Many Connecticut 

communities were severely damaged by floods in 

1955, stimulating much planning and development 

activity. Salmon Brook in East Granby overflowed its 

banks, destroying a vacation-cottage development 

which was being occupied year-round. The town

relocated the residents and converted the area into a 

park. Zoning and subdivision regulations were 

adopted in 1956, and a plan of development was 

adopted the following year. The area affected by the 

flood was included in a special flood-plain zone.

Several years ago the planning and zoning 

commission decided that the 1957 plan was no longer 

valid. It became apparent that multifamily housing 

was needed in East Granby, and this was not 

recognized in the old plan. Applications were being 

received for commercial establishments at locations 

scattered throughout the town, and it became 

necessary to reassess the town's commercial needs. In 

addition, just as environmental awareness was 

increasing generally throughout the Nation, the town 

of East Granby was experiencing interest in the 

conservation and preservation of special areas. 

Because of the shortcomings of the old plan and 

because of the new interests in town, the planning 

and zoning commission began to prepare a new plan. 

This work was undertaken with technical assistance 

from the Bureau of Local Government of the 

Connecticut Department of Community Affairs.

In preparing the new plan, the planning and zoning 

commission solicited the ideas, projections, and goals 

of other town agencies and mailed a plan of development questionnaire to all East Granby residents. The 

commission then adopted three overall goals which 

closely express the citizen response to the questionnaire. These goals were:

 "Maintain and enhance the rural character of East 

Granby."

 "Provide for a balanced growth of population, 

housing, commercial and industrial development. 

Develop the town facilities and utilities to serve 

planned growth."

 "Protect the natural resources and ecology of East 

Granby."

In order to give more detail to these generalized 

goals, the commission also adopted a series of goals 

and actions for 12 areas of concern. These areas 

include housing, commercial development, industrial development, agriculture, recreation, conservation and open space, community facilities, public 

utilities, town center, airports,quarrying,and historic 

preservation. Actions to be taken to reach these goals 

were also decided upon. These actions and goals 

were then combined with land-use information, 

socioeconomic data, and soil and geologic information to develop a picture of the town's future physical 

development.

Talcott Mountain Ridge

Sedimentary bedrock

Sand or sand 

and gravel

Basalt Clay

A geologic sketch of the landscape and 

rocks of East Granby.

47
Natural-resources

mapping and natural

land-use intensities

The natural-resource data used for the plan of 

development for East Granby were obtained from a 

detailed soil survey, surficial geologic maps, and 

hydrologic reports . A base map at a scale of 1:12,000 

(1 inch equals 1,000 feet) was prepared by splicing 

together and reducing negatives of the town assessor's property maps, and a topographic overlay was 

prepared by enlarging and splicing together sections 

of two U.S. Geological Survey topographic maps.

From the natural-resources data available, seven 

maps were prepared. Each map is discussed separately 

in the plan of development, which describes the 

impact of development on the natural factors and the 

impact of the natural factors on development. Five of 

of these maps showing unconsolidated materials, 

depth to bedrock, slope, areas having seasonal highwater table, and ground-water potential are presented here, at reduced scale. The two other maps 

one showing flood plains and one inland wetlands 

and watercourses are currently included in the 

town regulations but are not shown separately here. 

Their information, however, appears on the final map 

showing future land use (p. 51).

The natural-resources maps describe single elements of the natural environment that interact in 

response to the stresses of development. For 

example, the rapid percolation rates of sands and 

gravels may be a positive factor in the location of 

septic systems; however, if an area also has high 

ground-water potential, the rapid movement of 

waste liquid may have a harmful effect on the water 

supply. This problem would be further complicated 

if the area were one of seasonal high-water table. 

For another example, areas underlain by till generally 

have good foundation conditions. However, in areas 

of steep slope, and especially where water levels are 

high, till often is less stable, resulting in poor foundation conditions.

To assist in the analysis of the combined effects of 

the natural factors, the five natural-factor maps, plus

All maps compiled in 

February 1976

N

data on flood plains and major wetlands, were combined and summarized in the map (far right, opposite) 

showing natural land-use intensities, or potential. 

This map identifies areas with greater or lesser 

problems for development. For example, Talcott 

Mountain Ridge has limited land-use intensity owing 

to shallow bedrock and steep slopes. In contrast, 

the area just west of Bradley International Airport 

has high land-use intensity because it is in an area 

of sand and gravel (good drainage, good foundation 

conditions) and a moderate-yield aquifer (sewers 

could prevent pollution) and there are no wetlands 

to restrict development.

Till

Compact till 

r.~" '!..! Clay deposit 

^^H Sliderock deposit

Swamp

Sand or sand and gravel deposit

Unconsolidated materials

This map provides generalized information on the drainage characteristics, 

permeability, and foundation conditions of the surface materials. In general, 

compact till and clay have low rates of 

permeability and poor drainage characteristics; sand or sand and gravel and 

sliderock have high rates of permeability and good drainage characteristics; 

in general, clay, sliderock, and swamps 

have poor foundation conditions. Data 

from surficial geologic maps. Additional 

information on compact till from the 

soil survey.

Areas well drained 

High vyater table

1 to 2 months of the year 

High water table

2 to 12 months of the year

48

Areas with seasonal 

high water table

Seasonal high-water areas may present 

such development problems as wet 

basements and septic system failures. 

In addition, these areas are among those 

regulated by Connecticut's Inland Wetland and Watercourses Act (Public Act 

155 of 1972, as amended). Data from the 

soil survey.

Areas of slope in excess of 15 percent 

require special attention, since many 

problems may be encountered with 

septic systems, road alinement, surfacewater runoff, and so forth. Data from 

the soil survey, represent the average 

slope for a map unit. (In standard practice, slope is given in degrees and grade 

in percent; 0-3 percent = 0-1 °43'; 3-15 

percent = 1°43'-8°32'.)
Bedrock within 2 feet 

Bedrock within 10 feet ~ 

Bedrock deeper than 10 feet

Depth to bedrock

Those areas where bedrock is within 

2 feet generally require extensive engineering preparation. Areas where 

bedrock is within 10 feet may present 

problems with excavating foundations, 

installing and operating septic systems, 

installing underground utilities, and 

alining roads. Data from soil survey and 

surficial geologic maps.

 HH High yield (50 to 2000 GPM) 

l' v "1 Moderate yield (20 to 200 GPM) 

Low yield (less than 25 GPM)

MODE 

Sand 

Gravel. 

Till

MODERATE 

Compact Till LIMITED 

Compact TJII, 

Wetlands.CIay, 

Swamp

MODERATE 

O LIMITED

Compact Till 

Wetlands

, MOtfeflATE

SaixfS Gfcave>

Till

LIMITED 

/ Clay.WetlandstSwanp

Potential High with 

High Yield Aquifer 

Sand & Grave/ 

Danger of Pollution

Potential ewers 

SanrM Gravel 7 

Moderate,Yield / 

Aquifer .,' 

No Wetlands "

MODERATE 

Compact Till 

Some Shallow 

LIMITED Bedr

Shallow 

Depth to 

Bedrock 

Steep SI 

Talcott Mtn. 

Ridge

MODERATE 

$and & Gravel 

High Yield 

Aquifer

MODERATE 

Sand & Gravel

Natural land-use intensities map

This map indicates the relative suitability 

for development based on natural factors. 

Areas designated as high intensity probably have few site problems. Areas designated as moderate intensity are likely to 

have problems which require careful site 

planning. Areas designated as limited 

probably have severe problems which 

require extensive and costly site 

preparation.

Ground water potential

Units are shown in gallons per minute 

(GPM). Map indicates those areas of 

saturated sand and gravel most suitable 

for community water supplies, although 

actual yields of wells in these areas have 

not been confirmed by extensive testing. Because ground-water pollution 

could pose serious problems in these 

areas, development should be carefully 

planned. Data from hydrologic reports. 49
Future land use

By combining the natural land-use intensities map 

with the existing land-use map, the transportation 

plan, and the public utilities map, and incorporating 

socioeconomic data determined from the planning 

survey, the planning and zoning commission prepared a future land-use map. Talcott Mountain Ridge 

was designed for open-space acquisition and lowdensity residential use. Agricultural land was identified and will probably be given short-term protection 

through zoning. The aquifers and overlying marshes 

in the northwest were not given special consideration 

because they are adequately regulated under the 

Inland Wetland Act.

In keeping with the strong desire for a town center, 

commercial development and most of the highdensity residential development have been planned 

for the town center. The presence of a high-yield 

aquifer designates this area as one for moderate landuse intensity; sewer service, however, would reduce 

waste-disposal discharge and thereby help protect 

the aquifer. Another area in the western part of 

town was also designated for high-density residential 

development. This designation was based largely 

on natural land-use intensity factors. In addition, 

industrial area boundaries were established on the 

basis of the natural land-use intensities map and 

existing land use.

The inclusion of natural land-use factors in the 

planning process familiarized commission members 

and others with the natural characteristics of their 

town and the influence of those facts of nature on 

development. The preparation and adoption of the 

plan, however, does not end the process of planning 

or the usefulness of the information obtained in 

that process, for the plan itself must now be implemented and will need to be revised from time to 

time. The natural-factor maps are available and will 

allow town agencies and officials, landowners, and 

potential developers to obtain a good idea of the 

conditions they can expect to find in an area. These 

maps will not replace detailed site reviews, but rather 

will be the starting point for site reviews.

All maps compiled in 

February 1976

N

LIMITED

HioJi Yield Aquftjc__ 

L Swamp Wetlands

MODERATE

Tifl.Some 

& Gravel

"* J^ 

MODERATE^ .«

Potential Hgh with 

High Yield Aquifer 

Sand & Grave/ 

Danger of Pollution

Pbtyntial 

Sand 4 Gravel 

Moderate .Yield 

Aquifer,,' , 

No Wetlands /

f\ /

i r: IS' 1 i

. ' H -^MODERATE ,

Sand & Gravel : J^ :\ \ Compatt Tilt 

Low Yield Aquifer -./ 

Compact THI / Wetland 

^ /Some Shallow

LIMITED 

Shallow 

A'' / Depth to

Bedrock 

Steep 

Talcott Mtn. 

Ridge

ATE 

$and& Gravel 

High Yield 

Aquifer

MODERATE. "ji. i! *

Natural land-use intensities

50

Single family residential 

Multifamily residential 

^^M Commercial

I I Public (with appropriate label) 

t 1 Industrial 

Recreation

II Open space

Active farmland 

I- *-' -J; < Woodland 

____ Golf course and gun club 

F' '-'-M Mining trap rock

Existing land use
-=H Gas pipeline (CL & P) 

Gas pipeline (Tenneco) 

Existing sewer 

I | Possible sewer extension 

| | Fire hydrants

 . ! Power lines

Long line trunk (AT 8 T)

0 4000 FEET 

I I I I I

Public utilities

Existing arterial 

I* ! Existing collector

-^ Pern Central Railroad

Transportation plan

Residential-multifamily

Residential-one unit per acre

Residential-special review, less than one unit per acre

Town property and facilities

Town parks and open space

Neighborhood recreation area

Semipublic recreation and open space

Town center

Commercial

Industrial

Major wetland areas

Active agricultural land

Earth resource removal

Flood plain

Future land use

The future land-use map was made 

by combining the four maps on these 

pages, and considering the following 

socioeconomic factors:

 Population

 Housing

 Commerce

 Industry

 Agriculture

 Transportation

 Recreation, conservation, and 

open space

 Community facilities

 Public utilities

 Town center

 Airports

 Quarrying

 Historic preservation

51
Drainage-area 

maps

Background of 

their use

Drainage-area maps are important tools for wateruse and related land-use planning. In southern 

Connecticut, drainage divides define essentially 

closed hydrologic systems; maps delineating these 

divides can be used to assess the environmental 

impact of land-use and waste-disposal activities and 

to determine various streamflow characteristics. 

Technically trained people are needed to delineate 

drainage-area boundaries, to collect and compile the 

hydrologic information needed, and to review the 

resulting maps and reports. Great technical expertise 

is not always necessary, however, for one to use a 

drainage-area map for planning.

The map on the opposite page shows the boundaries and natural drainage areas of the major drainage 

basins in the Deep River quadrangle. It also shows 

sites where records of quantity and quality of streamflow are available. The boundaries of larger drainage 

basins are shown by the heavy lines, and the boundaries of smaller drainage areas by light lines. (The 

area drained by the Salmon River is shown by a 

pattern.) The measured drainage areas are those 

areas contributing to surface runoff. In most parts 

of New England, they are the same as those areas 

contributing to ground-water runoff. The drainage areas have not been adjusted for any manmade changes such as storm sewers, road ditches, 

culverts, diversion dams, canals, and tunnels. The 

effects of these changes in this example, however, 

are minor.

The three following examples illustrate some of 

the applications of drainage-area maps to planning 

in this part of Connecticut. The first two, concerned 

with site selection and environmental assessment, 

are based on drainage-area maps alone. The third 

example, concerned with streamflow characteristics, 

uses the drainage-area maps in combination with 

other hydrologic information.

Urban development and the disposal of urban 

wastes generally affect both the availability and the 

quality of water. Storm sewers and impervious surfaces such as roads, parking lots, and buildings 

increase the surface runoff to streams and reduce 

the amount of ground-water recharge. Waste-disposal 

operations and application of fertilizers and highway deicing chemicals have impaired surface- and 

ground-water quality at many places in the region.

Drainage-area maps can help in evaluating the 

suitability of sites for future development and in 

assessing the potential environmental impact. In 

areas such as the Deep River quadrangle, precipitation that falls on each drainage basin is the only 

source of inflow, and ground-water circulation is 

confined within the drainage area. The direction of 

ground-water movement is generally away from the 

drainage divides and toward the streams, lakes, 

swamps, and estuaries.

Example 1 evaluating

waste-disposal

conditions

The potential impact of waste disposal is a common 

problem in areas of proposed development. The 

effect of effluent discharge on local water quality 

depends on a number of factors. One of the most 

significant is the ability of the receiving waters to 

dilute the effluent. Information on the dilution 

capacity can be obtained from the drainage-area 

map.

A residential development of 400 homes is 

proposed in the area labeled example 1 on the map. 

The development will be served by a public watersupply system and sewers. Sewage, after treatment, 

is to be discharged to a nearby stream or to the 

ground. The map shows that those streams to the 

north have small drainage areas of 0.26 and 0.22 

square miles and therefore have a relatively low 

natural flow. Great Brook to the south, however, 

has a drainage area larger than 4.25 square miles and 

therefore several times the natural flow and much 

greater potential for waste-water dilution. Furthermore, discharge of sewage either to the ground or 

to streams in the northern part of the tract might 

contaminate Waterhouse Pond or Upper Pond. These 

impoundments would receive the nutrient-rich 

waste water with minimal dilution. No surface-water 

impoundments are located in the Great Brook basin 

to the south, but waste discharge could affect the 

balance of stream plants and animals.

Example 2 impact of

highway salting

on water quality

The environmental impact of highway salting is an 

important consideration for the planner and water 

manager. Highway deicing chemicals have, in some 

places, severely degraded existing water supplies 

and have also harmed roadside soils and vegetation. 

Qualitative assessments of the effect of highway 

salting on water quality can be obtained from the 

drainage area map and from data on salt application.

As rain and snow are rather evenly distributed 

throughout the mapped area, differences in average 

annual streamflow are due principally to differences 

in the size of the drainage area. The ratio of salt 

application to drainage area can, therefore, be used 

as an index of the relative impact of road salt on 

water quality: the higher the ratio, the lower the 

relative dilution. The ratio index can also be weighted

Nutrients flushed from residences 

and farmlands in New England 

often cause algal blooms in lakes 

and ponds.

where necessary for variations in average annual 

streamflow owing to factors other than drainage 

area. The following example uses the ratio between 

salt applied and drainage area to compare the relative 

effect of salting of Route 9 in the Pattaconk Brook 

drainage basin (site 2a on map) with salting of 

Route 9A in the Waterhouse Brook drainage basin 

(site 2b on map). Route 9 is a four-lane highway with 

single-lane ramps, and Route 9A is a two-lane highway. The average annual salt application per lane 

mile of highway is approximately 8.8 tons.

Route 9, Pattaconk Brook

Drainage area of Pattaconk Brook upstream of 

Jennings Pond (from the drainage-area 

map) ...................... 8.41 square miles

Lane miles of highway crossing the drainage basin 

(measured on the drainage area map).. .6.5 miles

Ratio of average annual salt application to drainage 

area (8.8 tons x 6.5 lane-miles 7 8.41 square miles) 

= 6.8 tons per square mile

Route 9A, Waterhouse Brook

Drainage area of Waterhouse Brook upstream from 

its mouth (from the drainage-area 

map) ...................... 1.37 square miles

Lane miles of highway crossing the drainage basin 

(measured on the drainage area map).. .2.0 miles

Ratio of average annual salt application to drainage 

area (8.8 tons x 2 lane miles r 1.37 square miles) 

= 12.8 tons per square mile.

This appraisal indicates significantly less dilution 

and more environmental impact from highway salting 

in the Waterhouse Brook basin. A more precise 

evaluation could be made using information on 

streamflow variability at the sites and salt applications 

per storm event. Relatively simple evaluations of the 

type described can identify potential problem areas, 

leading to detailed field studies and to subsequent 

alteration of the pattern of application of deicing 

agents, the kind of agent used, or the total quantity 

of agent applied.

Stream-gaging stations, as the one 

shown here. provide the basic 

streamflow information essential 

in land-use planning.

52
MISCELLANEOUS FIELD STUDIES 

MAP MF-524 C

UNITED STATES

DEPARTMENT OF THE INTERIOR 

GECLOGICAL SURVEY

V

^

EXPLANATION

Map shows stream systems and drainage 

areas that contribute streamflow to 

selected sites on streams.

Drainage areas shown have not been adjusted for the manmade changes in the 

natural regimens such as storm sewers, 

diversion dams, canals, and tunnels.

STREAM SYSTEMS

AREA DRAIHED BY THE SALMON RIVER 

(Tributary to the Connecticut River)

AREA DRAINED BY SMALLER STREAM SYSTEMS 

TRIBUTARY TO THE CONNECTICUT RIVER

DRAINAGE DIVIDE BETWEEN STREAM SYSTEMS

DRAINAGE-AREA BOUNDARY

2(1

TOTAL DRAINAGE AREA-' Number indicates 

area in square miles that contributes 

streamflow to selected site on a stream 

(area in square miles x 2.59 - area in 

square kilometers). Where the selected 

site is a mouth of tributary stream, 

generally two numbers and associated 

drainage-area boundaries are shown. One 

number is the square miles of drainage 

area of tributary stream at its mouth, 

and the other number is the square miles 

of drainage area of the larger or main 

stream immediately upstream from the 

mouth of tributary stream. The square 

miles of drainage area of the larger or 

main stream immediately downstream from 

the mouth of tributary stream is, therefore, the sum of the two numbers shown.

SELECTED SITES 

Symbols may be superimposed

STREAM-GAGING SITE

D 

SURFACE-WATER SAMPLING SITE

A

OUTLET OF SURFACE-WATER IMPOUNDMENT

o

MOUTH OF TRIBUTARY STREAM

X

SUPPLEMENTAL SITE

GENERALIZED DIRECTION OF STREAMFLOW

CONTOUR INTERVAL 10 FEET

DATUM IS MEAN SEA LEVEL 

DEPTH CURVES AND SOUNDINGS IN FEET DATUM IS MEAN LOW *

Drainage-area map of the Deep River quadrangle

53
Example 3 flood 

magnitude and

frequency in

designing bridges

and culverts

Design criteria for bridges and culverts require 

information not only on drainage areas but also on 

flood magnitude as related to flood frequency. Flood 

magnitude and frequencies for ungaged sites in 

Connecticut can be estimated from graphs relating 

floodflows to drainage areas.

Estimates of the floodflow at an ungaged site on 

an unregulated stream located in a virtually nonurbanized basin within this region can be determined 

from the graphs below. First, the drainage area is 

determined from the drainage-area map. The median 

annual flood is then estimated from the left graph 

and flows for floods of other frequencies are estimated from the right graph. The following hypothetical problem in culvert design illustrates this 

method.

An existing culvert at a site on Roaring Brook 

(example 3 on the map), which has a drainage area 

of 7.9 square miles, can convey a peak flow of 500 

cubic feet per second, but greater flows than this 

will be obstructed, thereby causing flooding upstream. A regional water-management plan proposes 

to reduce the flood hazard by replacing all culverts 

not capable of conveying the peak flows that will 

occur at average intervals of 10 years. Urbanization 

tends to increase peak flows. Therefore, replacement 

culverts should be designed to handle much larger 

flows, such as those which occur at average intervals 

of 100 years. Should the Roaring Brook culvert be 

replaced?

The median annual flood for a stream with 7.9 

square miles of drainage area is estimated from the 

graph at left to be 280 cubic feet per second. The 

annual peak discharges that will be exceeded at 

intervals averaging 10 and 100 years in length are, 

respectively, about 2.1 times the median annual flood 

or 590 cubic feet per second and 4.4 times the median

Engineering design of bridges and culverts is based on flood magnitude and frequency criteria.

annual flood or 1,230 cubic feet per second, as estimated from the graph at right. The existing culvert 

cannot convey even the 10-year floodflow and should 

be replaced. To avoid backup of water, the new 

culverts should be designed to handle an estimated 

peak discharge of 1,230 cubic feet per second.

Drainage-area maps can be used in conjunction 

with peak flow data and other hydrologic data in 

many other applications. Among such applications 

are the design of waste-treatment plants, watersupply reservoirs, flood-detention works, impoundments for power generation, and storm sewers; the 

siting of powerplants or other facilities with specific 

requirements of processing or cooling water; delineating flood-prone land, determining the suitability 

of rivers and estuaries for commercial fisheries, 

assessing water pollution; drafting water-quality 

standards and enforcing regulations; assisting agriculture; and providing information to be used in 

litigation over water rights. Examples of some of these 

applications can be found in the list of sources on 

page 94.

Relationship between drainage area and median annual flood 

in the lower Connecticut River basin

Flood magnitude frequency curve for the lower Connecticut

River basin

54
APPLICATIONS IN AN ATLANTIC COAST ENVIRONMENT I

> _-

lii! assa

^BS^f^^^^^^MM^VV Mm ~^VH4ft0BB^V*"l^^R^^V^ ^ ^H pngls ew

i t***+mimm\t t na ' i "^ I MM i ii i i i i i M^_^^^^r »HJ»^^tw

Water problems in humid country;

^3^MB^

TV \r

<*~r

' -~ ', * r k -L ^^^^*«^ 4

By B. L. Foxworthy]

Background of 

water use

Ground water has been a major continuing 

concern on Long Island, New York, for many decades. 

For most of the time since the arrival of the first 

European settlers, the population of the island has 

been completely dependent on local water resources 

for fresh-water supplies. The present aqueducts 

from the mainland to supply Kings and Queens 

Counties on western Long Island were completed 

only after intensive pumping from wells in Kings 

County had resulted in serious salt-water intrusion 

and a water-supply crisis. That crisis also led to legislation, in 1933, enabling the State to regulate the drilling 

of new wells on the island and requiring water conservation measures. The legislation was founded on, 

and certainly was one of the most important uses of, 

the then-existent information on the geology and 

ground-water conditions of Long Island.

Significant water-related problems still remain for 

Long Island, especially for Nassau and Suffolk 

Counties (see map), where a very large and still 

growing population remains dependent on ground 

water for virtually all fresh-water supplies.

The ground-water resource is capable of providing 

abundant good-quality water for the anticipated 

needs during this century and beyond. However, 

much depends on how well the ground water is conserved and protected from contamination. Wise 

planning and sound management to achieve the 

greatest benefit from this invaluable resource will 

require the best obtainable scientific guidance, 

including the kinds of information listed in the

LONG

Kings 

County'

JMassau 

County

.Queens 

County

Suffolk County

ATLANTIC

adjacent statement by Lee Koppleman, Executive 

Director of the Nassau-Suffolk Regional Planning 

Board. Examples in map form of the kinds of information that have been developed in response to that 

need, and how they were combined and applied, are 

presented on the following pages, focussed on the 

"middle" county of Long Island Nassau County.

Ground water has been used extensively in 

western Long Island for about 100 years, significant 

water records have been kept for more than 70 years, 

and intensive studies of the ground-water system 

have continued for about the last 40 years. Partly 

as a result, most of the laws, public policies, and 

plans for water management were already formulated 

and established at both the State and county levels of 

government by the 1950's. Consequently, although 

much additional geologic and hydrologic information has been needed and produced in the last two 

decades to improve the understanding of the 

ground-water system, that information has been used 

mainly to enhance the administration of preexisting 

plans and policies, rather than to develop new ones.

Unlike most of the other examples in this book, this 

chapter on Long Island cites few specific examples of 

governmental actions based on earth-science information. Using such information is a "way of life" on 

Long Island, which could well serve as a model for 

similar use elsewhere.

On Long Island, more than for most areas, a knowledge of the 

water resources and planning to ensure future dependable supplies of good-quality water are dominant elements in long-range 

planning.

At present [1975] about 2.8 million people in two counties on 

Long Island are entirely dependent on ground water for all their 

water supplies, and that part of the population is likely to grow to 

3.3 million by 1985.

The types of ground-water information that are most uieful in 

long-range planning for Long Island include:

1. Character and size of the reservoir of fresh water

2. Recharge of the ground-water system

3. Water-level changes associated with man's activities

4. Water-quality changes associated with man's activities

5. Problems of sea-water intrusion.

Lee Koppleman, Executive Director 

Nassau-Suffolk Regional Planning Board
The ground-water 

reservoir I

Long Island's fresh ground-water resource is one of 

the world's largest in terms of the volume of water 

and the number of people who use it. The rocks 

beneath the island constitute a huge reservoir, filled 

by nature over the centuries and now being 

manipulated by man. A basic requirement for 

interpreting man's impacts on the ground-water 

reservoir and for making sound management decisions about this resource is an adequate understanding of the ground-water system and how it has 

functioned over the years. This means understanding 

the ground-water situation under natural (predevelopment) conditions, the ground-water situation 

under present conditions, the geologic framework in 

which the ground water occurs and through which it 

moves, and how the water enters and discharges from 

that framework. The information needed to understand the shallow and deeper parts of the groundwater reservoir of Nassau County under essentially 

natural conditions are shown on these two pages and 

the next two. Information that pertains more to man's 

impacts on, and use and management of, the groundwater system is presented later.

The shallow part

Much of Nassau County is blanketed with deposits 

left by glaciers many thousands of years ago. 

These glacial sediments yield large amounts of water 

at depths of less than 100 feet. This shallow waterbearing zone, or aquifer, overlies other important 

aquifers in older rocks formed in the ocean 60-70 

million years ago. Different combinations of information are needed for understanding these different 

water zones. Some of the maps and cross-sections 

used to define the shallow ground-water system in 

Nassau County are shown here.

The shallow aquifer can be portrayed by combining 

three maps one of the topography (lower left), one 

of the geology (opposite, upper), and one of the 

altitude of the water table (lower right) with crosssections made up from logs of shallow wells (immediately below). The result of bringing this information 

together is a model of the shallow aquifer (opposite, 

lower).

Most of the water, fresh or polluted, that is added to 

the lower aquifers must pass through and leak out of 

the shallow aquifer. The shallow aquifer therefore

exerts strong controls on the recharge to, or replenishment of, the entire ground-water reservoir and on 

the movement of pollutants to it from the land 

surface. In following pages, we will see how the kinds 

of data shown here have been combined to guide a 

State and county policy for effective disposal of storm 

runoff in Nassau County through nearly 700 recharge 

basins. We will also see how water moves through the 

reservoir, and how our knowledge of its path makes it 

possible to trace pollutants in the ground water to 

their sources.

(268f eetbew and su rf aeT--~-- 160'

(Modified from Perlmutter and Lieber, 1970)

160'

Typical cross section in Nassau County

Subsurface data from shallow to moderately deep wells, including materials 

penetrated (strip patterns), position of water table, and different aquifer 

zones. Vertical scale is greatly exaggerated.

m U.S. Geological Survey 

New York 1:250,000, 1960)

Topographic map of Nassau County

Contours are in feet above mean sea level.

(Modified from Kimmel'. 1971)

Water-table map of Nassau County

Contours show the altitude of the water 

table, in feet, at vertical intervals as labeled. 

Dots show the location of wells used to 

measure the water fa6/e.

56
S I Beach, marsh, and swamp

3: I deposits; dune sand; alluvium

Harbor Hill ground Harbor Hill terminal Kame-delta deposits 

moraine deposits moraine deposits

Ronkonkoma terminal 

moraine deposits

Glacial deposits 

(undifferentiated)

Matawan Group and 

Magothy Formation

I I l I

10MILES

I I I I I

0 5 10 15 KILOMETERS

Geologic map of Nassau County

(Largely from Fuller. 1914)

Model of the shallow, upper glacial aquifer

This model was prepared by combining all 

the maps on these two pages.

Not to scale; large vertical exaggeration

(Modified from Cohen and others, 1970)

57
The ground-water 

reservoir II

The deeper part

Most of the fresh ground water for Long Island 

comes from layers of sand below the shallow aquifer, 

at depths generally greater than 100 feet below the 

land surface. Most of our knowledge about the 

deeper aquifer zones in Nassau County has come 

directly or indirectly from the records of several 

thousand wells. From these well records, the logs, like 

those shown below, were used to prepare maps of the 

top and bottom of each lower aquifer unit. The maps 

on the facing page are of the largest deep aquifer, the 

Magothy. Similar maps have been made of the other 

deep aquifers, of non-water bearing layers, and of the 

surface of the ancient bedrock beneath. A threedimensional model (facing page) of the natural 

ground-water system has been developed by combining all these maps with those maps (upper right) 

which produced the model of the upper glacial 

aquifer.

Although the deeper aquifer zones are generally at 

least 100 feet below the land surface, the water levels 

in the deeper wells, as represented by the contour 

map on the facing page, are much shallower 

generally less than 50 feet below the land surface. This 

apparent anomaly exists because water in the deeper 

sand units is confined under artesian pressure, 

causing it to rise in wells to a level higher than the top 

of the sand layers. Water that enters the deep aquifer 

where it is near the surface at the north side of the 

island (see model, bottom opposite page) moves 

downward and southward within the sandy layers that 

are beneath discontinuous layers of clay and silt, 

which retard upward leakage. Wells that penetrate 

the clay and silt layers and tap the sand aquifer 

provide a conduit through which the water under 

pressure can rise above the sand layers to a level of 

equilibrium.

The conceptual model of the ground-water 

reservoir, while lacking the elegance and flexibility of 

a mathematical model such as that described earlier 

for El Paso County, Colorado, has been a reliable basis 

for detailed study of the ground-water system, 

leading to decisions regarding the management and 

conservation of the priceless fresh water. For 

example, the model has been used:

 To locate parts of the system to which pollutants 

had not yet migrated so that a picture of predevelopment water quality could be reconstructed.

 To estimate the decline of ground-water levels and 

probable reductions in streamflow caused by 

present and planned sanitary sewer construction.

 To estimate the quantity and quality of available 

water supplies.

 To help formulate and judge several alternative 

schemes for long-term management of the fresh 

ground water, discussed later.

- r-''

N K J ; )t_

j" v* ^liiiiiillllllffl^^^^^^^

I £* Topographic map 

i

.>

Map group for the shallow part of the ground-water reservoir

These three maps represent those on the 

previous two pages from which the model 

of the shallow, upper glacial aquifer was 

derived.

SOUTH 

100' -i

NORTH

SEA LEVEL

100' - -

200' - -I300' - I400' --

Typical cross section in Nassau County

Wells (strip patterns) penetrate various 

aquifer and nonaquifer zones. Vertical 

scale is greatly exaggerated.

500' - -_-;

600' -~-

700' 

800' 

900'

(Adapted from Ku and others, 1975)

-SEA LEVEL

100'

200'

:-!- - 300'

i - 400'

 500

-600'

 700'

 800'

900'

58
1 I

(Modified from Kimmel, 1971)

Water-level contours (in feet) for deeper (Magothy) aquifer

Dots indicate location of wells used to 

derive the measurements.

0 5 MILES I I I I I I

(From U.S. Geological Survey unpublished map, 1960)

Thickness of Magothy aquifer, in feet

Model of the structure, form, and functioning of the 

ground-water reservoir of central Long Island

FRESH GROUND. WATER

^*feN?..

:.;'.''.'... Magothy aquifer

-.: ;..,: : SALTY .GROUND. WATER;;

Not to scale; large ^ertieal

(Adapted from -Cohen and others, 1970)

59
Recharge and 

discharge

The ground-water reservoir acts as a water bank for 

the people of Nassau County. Like a financial bank, it 

receives "deposits" (recharge) and has "withdrawals" 

(pumpage and natural ground-water discharge), and 

it also has "reserves" in the form of huge volumes of 

fresh water stored in the ground. As with a financial 

bank, effective management of the water bank and 

planning for its future require the best possible 

knowledge of the deposits (recharge) and withdrawals (discharge), as well as the reserves (water in 

storage). These two pages summarize the ways in 

which recharge and discharge information about the 

Nassau County water bank has been compiled and 

applied.

Recharge

To understand the recharge situation in Nassau 

County today, consider the natural recharge to the 

ground-water reservoir, pictured in the group of 

maps to the upper right, and man-caused changes to 

the natural recharge, pictured in the group of maps 

to the lower right. Rain and melted snow which 

infiltrate the ground are the main sources of water for 

Long Island, as they were before man, and the deeper 

aquifer zones are still replenished mainly by ground 

water passing downward from shallow zones. However, the ways in which the water reaches or does 

not reach the ground-water reservoir have been 

greatly affected by man's activities.

Urban development in the county has resulted in 

increased recharge at some places and decreased 

recharge at others. Where the normally permeable 

soil has been covered extensively by buildings, 

pavement, and other impervious materials, recharge 

to the shallow aquifers has been reduced. Recharge 

to shallow aquifers also has decreased in parts of the 

county where household sewage disposal has been 

changed from individual cesspool and septic tank 

systems, which returned the waste water underground, to sewer systems that eventually discharge 

the waste into the ocean.

The widespread use of excavated, unlined pits, or 

"recharge basins" for disposal of storm-runoff water 

(see photograph opposite) probably causes enough 

recharge to the shallow aquifers to more than offset 

the decreases caused by pavement and other 

impervious surfaces built by man. However, the 

recharge through the basins is very different in 

distribution, in rate of movement, and in quality than 

it was under natural conditions.

Disposal wells, which are required by State law for 

the return of most ground water used for such 

purposes as cooling, artificially recharge both the 

shallow and deeper aquifers. In addition to changing 

the natural patterns of recharge, discharge, and 

movement of the ground water, many of these 

disposal wells commonly return water to a different 

aquifer than the water was pumped from, and return 

the water at an unnaturally high temperature. The 

balance of the ground-water system has been further 

upset by intensive pumping from wells.

The recharge information summarized in the map 

groups is being applied to needs such as planning of 

land-use densities, including preservation of open 

space, tracing the paths of pollutants in the groundwater system, and analyzing causes of changes in 

ground-water levels. Perhaps most important, the 

recharge information plays a key role in various 

alternative schemes for long-term management of 

the ground-water reservoir, which are discussed on 

page 68.

The information obtainable, including the effects 

of the Northeast drought of 1962-66, indicates that 

the amount of the recharge to the shallow aquifers is 

about as it was under natural conditions, except in the 

sewered area of Nassau County where it has 

decreased measurably since about 1953. Thus, in most 

of the county, the deposits to the water bank have not 

been much changed by urban development. In the 

next discussions, we see how the withdrawals and 

reserves of the water bank have been affected.

Lines of equal precipitation, 

in inches per year

(From Miller and Frederick, 1969)

Surficial geology

£TOU>

Natural factors controlling recharge 

to the ground-water reservoir

Before man intervened, recharge to the 

ground-water reservoir was wholly controlled by natural factors, mainly those 

represented here as layers of map data. 

Even with significant changes caused by 

man, these data are still essential to understanding the recharge process.

\

Man-caused changes to the 

natural recharge

Data include different disposal methods 

for sewage water, recharge basins for 

handling storm runoff, and disposal wells 

for returning water to the ground after 

using it for cooling.

60
A typical recharge basin in Nassau County

Discharge

Even before man, the ground-water reservoir 

constantly lost water, to the air and to the ocean, as 

shown in the diagram at right. Most of the water 

that infiltrated the land surface and recharged the 

ground water moved laterally through the shallow 

aquifer and discharged to streams or the salt water 

without ever reaching the deeper aquifers. Water in 

the deep aquifers, after moving downward from 

shallower zones in the central and northern parts of 

the county, reversed its flow in south-shore areas and 

discharged water by upward leakage to shallow 

aquifer zones, as shown by the small arrows on the 

diagram. The other major form of fresh-water 

discharge from the deep aquifers was the mixing with 

and assimilation into adjacent salty ground water 

(discussed later, p. 66).

Urban development in Nassau County has added 

another major form of ground-water discharge the 

large-scale pumping from wells for industrial and 

public water supplies. Most of the pumping is from 

the deeper aquifers. The intensive pumping from 

those aquifers has increased the rate of downward 

leakage from the shallow aquifers at places. Similarly, 

the natural upward leakage from the deeper aquifers 

has decreased at other places, mainly in the southern 

part of the county.

Besides managing the artificial ground-water discharge the pumping and other discharge caused by 

man it is also possible to affect the natural discharge. 

For example, making major withdrawals from the 

water bank results in the interception and use of some 

ground water that otherwise would discharge to the 

sea or sky without serving man. The ability to modify 

the natural discharge by using artificial discharge 

(mainly pumping) and adequate knowledge of the 

ground-water reservoir is fundamental to several of 

the long-term water-management alternatives being 

considered for Long Island (discussed later, p. 68).

The information available on ground-water discharge includes: 

Pumpage amounts Required by the New York State

Department of Environmental Conservation (see

graph to the right). 

Distribution of pumpage Locations of pumped

wells and identification of the aquifers tapped by

those wells.

1. Seepage to streams

2. Subsurface outflow

3. Evapotranspiration

4. Spring flow

General movement of 

fresh ground water ^.- C| ft

FRESH GROUND WATER

(Modified from Cohen and others, 1968)

Natural modes of ground-water discharge

These modes and the pumping from 

thousands of wells constitute nearly all 

discharge in Nassau County.

Streamflow measurements The most reliable of all 

available data on the various kinds of natural 

discharge.

Estimates of subsurface outflow Rough calculations 

based on knowledge that has been developed 

about the ground-water reservoir and how water 

moves through it (see previous four pages). 

The major uses of the information on discharge are 

for regulating pumping in accordance with New York 

State regulations and for evaluating long-term watermanagement alternatives.

As we shall see in the following two pages, 

information on water levels and their changes has 

been instrumental in understanding the variation of 

the reserves in and withdrawals from the Nassau 

County water bank, as it has been in understanding 

other aspects of the water bank.

250

200

(Modified from Cohen and others, 1968)

=! Q

150

UJ (/)

9: 2 100

O

a: 

o

50

61
Water-level changes

Many of man's and nature's influences on the 

ground-water reservoir are reflected in water-level 

changes. On Long Island, records of changes in 

ground-water levels, plotted on maps, have been 

essential tools for water-related predictions and 

planning.

Water levels measured about the same time in a 

network of observation wells are commonly shown 

on a map in the form of water-level contours that is, 

lines of equal water-level elevations for the entire 

county. A water-level contour map for a specific 

aquifer zone, such as that to the right, is used to 

determine the general pattern of movement of 

ground water, and of any contaminants it may 

contain. Similarly, water-level contour maps for 

shallower and deeper aquifer zones are regularly 

compared to find where water is moving between 

aquifer zones. For this discussion, only data for one 

deep aquifer zone are shown; similar data are available and used for the shallow aquifer and for the 

other deep aquifers.

Where ground-water conditions are not much 

affected by man's activities, changes in ground-water 

levels are relatively small and reflect mainly the 

seasonal and year-to-year differences in recharge 

from precipitation. This means that, under natural 

conditions, the ground-water reservoir was in 

balance, with discharge about equaling recharge in 

other words, the reserves of the water bank were 

relatively constant. The greatest recorded natural 

changes in water levels were a decline of more than 10 

feet in shallow aquifers in the central part of the 

county during the severe drought of 1962-66 and a 

general rise to virtually average levels by the early 

1970's. In shallow aquifers nearer the shorelines and 

in the deep aquifers, the water-level changes 

attributed to natural causes are much less, commonly 

less than a foot or two.

Water-level declines

Man's activities have produced much greater 

changes, the most critical of which are declines of 

more than 20 feet (by 1970) that are widespread in the 

deep aquifer zones (see maps to right and below). 

The distribution and amount of the declines were 

determined by comparing water-level contour maps 

for different times and compiling the water-level 

differences in the form of "net-change" maps. Netchange maps for different aquifer zones also are 

compared to analyze the similarities or differences 

in water-level changes within different parts of the 

ground-water reservoir.

The amount and distribution of major water-level 

declines, as well as the aquifer zones involved, are of 

critical concern to the water planner and manager. 

Such major declines represent decreases in the 

amount of storage in the ground-water reservoir in 

the reserves of the water bank. They diminish the 

future adequacy of water supplies, change the 

movement of water (and contaminants) through the 

ground-water reservoir, and, in nearshore areas such 

as parts of Long Island, decrease the natural discharge 

by subsurface outflow and increase the threat of saltwater intrusion. However, little can be done to 

reduce or otherwise respond to such declines until 

their causes are known.

DETERMINING CHANGES

Comparison of water-level declines 

and probable causes

Comparing the decline map above with 

the maps representing likely causes of the 

decline, shown here, provides insight 

to the relative importance of each possible 

cause.

Water-level contours, deep 

aquifer, 1970, in feet above 

mean sea level

[^I ^ Deep observation-well data

Water-level contour maps

Monitoring the amount of water in Nassau 

County's ground-water reservoir includes 

periodic comparison of water-level contour maps, such as the top and bottom 

map layers of this figure. These are derived 

from water levels measured in selected 

observation wells (middle map layer).

5 Water-level contours, 

deep aquifer, 1959

(Kimmel, 1971)

INTERPRETING CHANGES

Water-level decline, 

in feet

0-5

Water-level decline map

20-50

The water-level maps above yielded this 

map of water-level declines in the deep 

observation wells during 7959-70.

Modified from Kimmel, 1971)

EVALUATING CAUSES

\ Distribution of pumpage, deep 

"" aquifer, in million gallons 

per day

Changes in recharge from 

shallow aquifer

Hydraulic character of deep aquifer
Causes of water-level declines

In Nassau County, the declines in ground-water 

levels have had several causes, some major and 

continuing, others minor and temporary. The relative 

importance of each has been estimated by graphically 

comparing the distribution of the decline to the 

distribution of the presumed cause. A simple example 

is a comparison of the net-change, or net-decline, 

map for the deep aquifer zone (facing page, middle) 

with a map showing distribution of pumpage from 

the deep zone (facing page, bottom).

The comparison demonstrates that intensive 

pumping from deep wells in and adjacent to Nassau 

County is the main cause of water-level declines in 

the deep aquifer zone. Another possible cause of 

decline is a decrease in recharge to the deep zones at 

places where the decline of levels in shallower zones 

has been comparatively large.

Water-level contour maps, because they can be 

translated into patterns of ground-water movement, 

have been widely used in Nassau County to trace 

contaminants in the ground water (see p. 64-65) and 

have thus been instruments in water-quality surveillance and enforcement of public-health regulations.

Knowledge of the water-level declines caused by 

the shift to sewer systems in southwestern Nassau 

County has warned officials of what to expect when 

other areas are sewered.

Relationships that have been found between 

pumpage and water-level declines have been used 

for many management and predictive purposes, such 

as:

 Predicting long-term water-level declines that are 

likely to result from providing water supplies to 

future population.

 Estimating changes in the rates of water movement 

within the ground-water reservoir.

 Determining the needs for, and timing of, future 

water-conservation plans, such as artificial recharge.

 Decisions, during the severe drought of 1962-66, 

to allow virtually unrestricted use of well-water 

supplies in Nassau County while New York City's 

stream-water supplies from upstate New York 

were sharply curtailed; also a decision to use a 

shallow-well system in Nassau County for emergency water supplies for New York City.

 A prohibition on the development of additional 

water supplies from the deepest (Lloyd) aquifer, 

except in near-shore areas that have no other 

dependable source of fresh water.

Artificial recharge test facility at Bay Park

Water-/eve/ recorders in foreground measure 

water-level changes in observation wells tapping 

different aquifer zones.

Typical continuous water-level recorder attached to 

an observation well

As the water level in the well fluctuates, a float 

causes the drum to rotate. A pen driven by a 

clock (in box in front of drum) moves horizontally across the rotating drum, keeping a continuous record of the water level.

63
Contamination

Contamination of the ground water is probably the 

most serious element in the planning and management for Nassau County's present and future water 

supplies. We tend to think that all contamination is 

caused by man, but this is far from true. From the 

moment a raindrop or snowflake falls over Nassau 

County, it is assailed by natural contaminating 

influences, displayed below on the now-familiar 

model of Long Island. These influences must be taken 

into account in attacking water-quality problems. 

Most of the county's water-quality problems, however, do result from human activity at or near the land 

surface (see maps to the upper right); for example:

 Storm runoff carries contaminants into recharge 

(disposal) basins, where some of them percolate 

down to the ground water.

 Household sewage enters the shallow aquifers 

through leaky sewer pipes and many thousands 

of cesspools and septic tanks.

 Precipitation leaches contaminants of many kinds 

from solid-waste disposal sites and carries them 

downward into the ground water.

 Some industrial disposal basins and wells have 

provided routes for contamination of the ground 

water.

 Contamination results from accidental spills and 

casual dumping of contaminating materials.

 Even the precipitation that recharges the ground 

water is often more acidic than it was in preindustrial days. It also contains other pollutants 

such as heavy metals and hydrocarbons, some 

of which are toxic in rather small concentrations.

 Other important sources of contamination are 

automotive wastes, excessive and improper application of road salts, pesticides, and fertilizers.

Once in the ground water, the contaminants move 

along the flow paths in the ground-water reservoir 

(upper diagram on facing page) and are superimposed on the water-quality patterns established by 

nature. Periodic chemical analyses of water from 

deep wells have shown, however, that contamination 

is spreading into the deep ground water which 

formerly contained very small amounts of dissolved 

material (lower diagram and map on facing page). The 

contaminants are being carried to the deeper aquifers 

by the shallow ground water that recharges the 

deeper zones. The downward movement of the 

contaminants has been increased by a lowering of the 

deep ground-water levels as a result of intensive 

pumping.

Temperature increases, a special kind of groundwater contamination, result partly from the recharge 

through cesspools and recharge basins, but mostly

Population density

POPULATION DENSITY,

IN PERSONS 

PER SOU ARE MILE

1000 - 1999

2000 - 4999

5000 - 9999

Sewered area

) ;; :. ,: :- **- 

(Cohen and others, 1968)

(Franke, 1968)

Disposal wells

v- ' ' \ V .-.'. -: . ...v. \

N xt. . ' "..... ,

j*:s&' '.-...-. \ I - ; -:V:.'- ' \

(Cohen and others, 1968)

Man-caused contamination sources

The kinds and degree of man-caused contamination in Nassau County depend 

upon local situations, such as those shown by the four maps above.

through disposal wells that inject warm or hot water 

underground following its use for air conditioning 

and industrial cooling.

Another special kind of ground-water contamination in Nassau County, related mainly to groundwater pumpage, is salt-water intrusion, discussed on 

pages 66-67.

The spread of contamination in the deep aquifer 

zones is a major concern because these zones yield

nearly all of the county's public water supplies. 

Sound planning for future water supplies requires 

reliable information about the types and degree of 

contamination, as well as predictions of when and 

where additional contamination is likely to appear. 

Such information is obtained by combining waterquality data, ground-water flow estimates, and the 

model, shown earlier, of how the ground-water 

reservoir functions.

Ground-water contamination on Long Island 

under natural conditions

7~o deal effectively with man-caused contamination, we must understand and take into 

account natural conditions which affect water 

quality.

Air moving over the ocean 

picks up salty spray

Rain and snow pick up dust 

and gases from the atmosphere

Evaporation and transpiration 

of precipitation from the land 

surface and from the soil zone 

increase the dissolved-solids 

content of the water

Physical, chemical, and biological processes modify the 

dissolved-solids content of the 

water percolating through the 

zone of aeration

Flow through sedimentary 

deposits in the zone of saturation modifies the total dissolved-solids content of the 

ground water only slightly

Physical, chemical, and biological process modify the 

dissolved-solids content of 

streamflow

Fresh stream water and salty 

water mix in estuarine reaches

Fresh ground water and salty 

ground water mix in the zone 

of diffusion

x

->"-r-aF>K\?i'y- ' '" -'-' - - -* " - "- "

FRESH GROUND WATER

(Cohen and others. 1968)

64
nofH 

NRH^ Disposal basin or landfill

>4 

>,"f^

Localized contamination routes in Nassau County

Contaminants that reach the ground water 

move along the general paths of groundwater flow (arrows), spreading in the form 

of "plumes" (red pattern). A major effect 

of most disposal wells is the addition of 

heated water (yellow pattern).

(Modified from Perlmutter 

and Lieber, 1970)

600' 

800' -

VERTICAL SCALE IS GREATLY EXAGGERATED

Regional contamination routes 

in Nassau County

From the shallow ground water, contamination reaches the deeper aquifer zones with water recharging the 

deep zones (cross-sect/on). In this 

way, contamination is spreading in 

Nassau County, as shown by the 

extent of high concentrations of 

dissolved nitrate in deep zones (map). 

The zone of greatest concentration 

is beneath an area of dense suburban 

population that adds nitrates in 

cesspools, septic tanks, and fertilized lawns.

(Modified from Perlmutter 

and Koch, 1972)

Map applications

Here are some specific examples of ground-water 

contamination problems attacked with the help of 

maps:

Detergents

Household detergents in the ground water, though 

not known to be health hazards, indicate the 

presence of household sewage. Data on the widespread presence and the movement of detergents 

in the shallow ground water led to the establishment 

of recommended limits for the amount of detergent 

compounds in public water supplies. The data also 

caused strong public and official reactions that were a 

major factor in decisions by the detergent industry 

to produce detergents that are more biodegradable 

than those formerly sold.

Deicing salt

Salt used to deice highways has contaminated the 

ground water in some places. But snow-melt water 

containing highway deicing salt was found in one 

study to be "fresher" than the ground water it 

entered. This unexpected finding results from the 

extensive contamination of the surrounding ground 

water from other sources and was used to support 

decisions to continue use of deicing salt.

Nitrate

Dissolved nitrate compounds from household 

sewage and other sources have caused water from 

some public-supply wells to exceed recommended 

limits for nitrate in drinking water. Knowledge of the 

movement of the contaminants through the groundwater reservoir has allowed identification of source 

areas for the nitrate (diagram to the left) and of 

aquifer zones where nitrate content is likely to 

increase. The data also have provided a basis for 

selecting as alternative water supplies aquifer zones 

and wells that are less likely to be contaminated.

Industrial and solid wastes

Industrial waste products, such as metal salts and 

organic chemicals, as well as leachate from solidwaste landfills, have reached the ground water 

in concentrations considered to be undesirable. 

Knowledge of the presence and movement of these 

contaminants has assisted officials in setting recommended limits for concentrations of certain dissolved 

materials in public water supplies, tracing the 

contaminants to their sources and imposing regulations to reduce future contamination, warning 

against taking drinking water from wells within the 

plumes of contamination, and ordering the cessation 

of pumping from certain public supply wells that tap 

contaminated aquifer zones.

65
Salt-water intrusion

Because fresh-water supplies on Long Island are 

obtained from aquifer zones below sea level, water 

use is accompanied by the threat of salt-water 

intrusion that is, the landward movement of salty 

ground water beneath the ocean into fresh-water 

aquifers beneath the land. At places in Nassau 

County, and especially in Kings and Queens Counties 

in western Long Island, salt-water intrusion has been 

more than a threat, it has been a harsh reality. Sound 

management and conservation of the fresh-water 

supplies, as well as effective long-range planning, 

require the reliable prediction of salt-water problems under various management schemes.

The relationship between fresh and salty ground 

water along the sea coast depends not only on nearshore conditions but also on any large changes, as in 

recharge or pumping, elsewhere in the ground-water 

reservoir. No extensive impermeable barriers in 

western Long Island separate the fresh ground-water 

reservoir from adjacent salty ground water, and the 

salt water is held in check only because large amounts 

of fresh water are constantly flowing seaward to mix 

with and discharge into the surrounding bodies of 

salty water, as the diagrams (right) show. Anything 

that reduces the outflow of fresh ground water allows 

salty ground water to intrude landward through the 

aquifers.

Two parts of Nassau County where troublesome 

salt-water intrusion has occurred in the deep aquifer 

zones (the main source of water supplies) are in the 

northwestern part (at Kings Point) and in the southwestern part of the county (see top map, opposite). 

Where it is invading the fresh-water aquifers, the saltwater front does not have the smooth shape that is 

shown in the preceding generalized models of the 

ground-water reservoir. Instead, it invades as a series 

of tongues, or wedges, moving along the more 

permeable aquifer layers toward the intensively 

pumped wells farther inland.

Monitoring the salt-water 

front

The lower illustrations on the opposite page show 

the approximate position of the salt-water front in 

a deep aquifer as interpreted in the late 1960's. The 

salt water in the deep aquifers was then thought to 

be advancing slowly along a rather broad front, 

presenting a threat to much of southern Nassau 

County. More recent information, including data 

from offsh >re drilling, now indicates that the saltwater front in the deeper aquifers is considerably 

farther offshore along most of southern Nassau 

County, although no map has yet been compiled to 

show the revised location of the front. Therefore, 

the threat represented by salt-water intrusion in 

southern Nassau County, at least in the near future, 

probably is mainly to the shallower near-shore zones 

and outlying areas such as islands and peninsulas.

Monitoring the salt-water front and predicting its 

position has required information on and interpretations of such things as the salinity of water from the 

aquifer zones that are likely to be affected (requiring 

sampling and chemical analysis), pumpagefrom wells 

tapping those aquifers, and water-level changes in 

those wells. To be effective for management and 

planning, all these data must be combined with an 

adequate understanding of how the ground-water 

reservoir functions.

North

North

B I 

South 

B'

Sea ,5 fland surface

leve ' «! Water table

 ;"v;";:.vl"":*'"v« Fresh I

:::.: :-/"'//;'I;Salty water;

(From Cohen and others, 1968)

Responding to 

intrusion

One possible response to salt-water intrusion is 

simply to shut down the pump on the salty well and 

find an alternative water supply, probably farther 

inland. This was actually done at Kings Point and at 

places in southwest Nassau and southeast Queens 

Counties. Or intensive pumping can be partly offset 

by adding more water to the aquifers between the 

salty ground water and the threatened well or wells.

Boundaries between fresh and salty ground water

Generalized boundaries between fresh and sa/ty 

ground water and natural movement of water along 

the south shore of Nassau County (upper left), in and 

near the zone of diffusion, which separates fresh 

ground water from salty ground water (upper right), 

and on eastern Long Island (below).

Proposals for artificially recharging the aquifers to 

conserve fresh water and thereby prevent or slow 

salt-water intrusion are basic parts of some of the

long-term water-management alternatives that have 

been considered for Nassau County, and which are 

discussed in the concluding section.

66
Kings Point

intrusion

Among the information needed to monitor the salty ground water (red areas) and 

predict its movement are repeated measurements of the salt content and of water 

levels in the affected aquifer zones and 

data on the amount and distribution of 

pumping from those zones.

i Salinity of ground-water

NORTH 

Sea level

300-

600-

900-

1200-

Shallow salty ground water

Upper glacial aquifer

-7 Gardiners Clay

jameco , Intermediate

\ aquifer ' salty-water

\ / wedge Magothy aquifer (Fresh water)

(Fresh water)

Deep satty-water wedge

itan c[ay -"-~-_"}-~-" -"~ _-

Lloyd aquifer 

(Fresh water)

EXPLANATION

Approximate landward limit 

of deep salt-water wedge

-6-

QUEENS ' NASSAU 

COUNTY . COUNTY

20-

Water-level contour

Shows altitude of water level 

above mean sea level

1012 MILES 

1,1 I I

Landward extent of salty ground water

Near the southwestern corner of Nassau 

County as interpreted in the late 1960's, 

salty water was farthest landward near the 

centers of pumping from a deep aquifer 

(cross section), where the water levels 

were drawn down the most (circular depressions in the water-level contour lines). 

Data now available indicate that, for areas 

east of the line of section (line A-A'on the 

map), the salt-water front actually is considerably south of the position shown here.

(From Cohen and others, 1968)

67
Long-term water

management

alternatives

Increases in the demand for water supplies, and 

deterioration in ground-water quality, are forcing 

critical decisions to be made about the continued 

development and future management of Nassau 

County's ground water. Sound and effective management will require the wise application of all the 

information previously discussed knowledge of the 

ground-water reservoir and how it functions, of 

recharge and discharge of the fresh water, and of 

present and threatened contamination, including 

salt-water intrusion.

Several major alternative methods of developing 

and managing the water resources of Nassau County 

have been proposed. Three contrasting schemes are 

outlined in the diagrams below. Nassau County has 

spearheaded intensive studies of the feasibility of

artificial recharge using water reclaimed from sewage 

as a means of conserving the fresh ground water of 

the county. Such artificial recharge would be an 

integral part of the barrier injection wells scheme 

(diagram below center) and an alternative scheme 

for returning the reclaimed water in the middle part 

of the county. The studies have used all the kinds of 

information mentioned here and have also included 

construction of a tertiary sewage-treatment plant at 

Bay Park to supply injection water; analysis of the 

subsurface geology and ground-water conditions in 

the vicinity of the injection well; and numerous 

experiments in which the highly treated sewage-plant 

effluent has been injected into a deep aquifer zone at 

Bay Park through an elaborate experimental well. As 

part of an evaluation of the barrier injection wells 

scheme, the studies also included analysis of the subsurface conditions along the proposed alinement for 

such recharge wells. To date (1977), these studies 

represent the most positive local action to meet the 

need for fresh-water conservation in the face of an 

expanding demand on the Long Island ground-water 

reservoir.

Since the studies were begun in the Bay Park area, 

two changes have occurred to shift the emphasis in 

water-resources management and planning for 

Nassau County. One is an increase in cases of waterquality degradation in the deep aquifers, as described 

in the discussion of ground-water contamination. The 

other is the finding of the apparently decreased threat 

of salt-water invasion of the intensively pumped 

deeper aquifers (see previous two pages). The major 

impact on water management and planning that 

these changes represent is to demonstrate the high 

value of authoritative, up-to-date information when 

planning involves a dynamic natural system such as a 

ground-water reservoir.

The stakes in conserving the fresh ground-water 

reservoir are high. The final selection of one or more 

water-management plans for the county doubtless 

will be guided by economic, political, sociological 

and other factors. However, choices based on the 

best obtainable scientific information about the 

ground-water reservoir and geologic framework 

offer the best hope for the future water resources of 

Nassau County.

Permit salt-water intrusion Inject treated water as a barrier Skim fresh water from shallow wells

Skimming wells Skimmingwells

Permitting the salt water to move inland to 

new equilibrium positions could substantially increase the long-term fresh-water 

yield.

Recharging the reservoir with highly 

treated sewage-plant effluent (T) by means 

of a network of injection wells could check 

contamination by salty water and increase 

the long-term fresh-water yield.

Drilling shallow wells to "skim" the water 

that now discharges into streams would 

increase long-term fresh-water yield if side 

effects could be tolerated.

NORTH SOUTH

FRESH GROUND WATER

Some water-management alternatives

General patterns of recharge from the land surf ace and movement of fresh water 

through the ground-water reservoir under natural conditions (large section 

above) and under three alternative schemes for long-term management of the 

reservoir (small sections above). The most thoroughly evaluated scheme is the 

one of barrier injection.

68
> -'V

PPLICATIONS

 rr>J '":ir vJ*v<Hr^ «r^>%*^><2^

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AN ATLANTIC CO^ST ENVIRp

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Fairfax County

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ounty. Virgin!

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^^^^ ^^ ^k1 A. J. Froeliclr, U.S. Geological Survey/A: D. Garnaas, Office 

- Comprehensive Planning, Fairfax County, Virginia; an<

/an Driel, U.S. Geological Survey

of

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Background of the 

project

An application for development of more than 1,000 

acres of undeveloped land into a high-density new 

town in the Franconia area of Fairfax County, Virginia, 

was rejected in 1972 by the County Board of 

Supervisors. In early 1975, however, rezoning for 

lower density planned development housing on the 

site was approved on the recommendation of the 

county's Office of Comprehensive Planning. In mid1975, a conceptual development plan (below) was 

submitted to the county for review. Subsequently, a 

revised conceptual development plan, which incorporates most of the county's recommendations, was 

submitted for approval in mid-1976. The main reasons 

for the county's subsequent approval were that the 

proposed new community could now be integrated 

with existing land-use and available public facilities 

and that development would be tailored to the 

natural limitations and opportunities inherent in the 

site. Newly available earth-science maps and related 

geotechnical data were used by the county environmental planning staff to analyze the rezoning 

application; this information was used even more 

extensively to modify the development plan so that it 

became more acceptable to all interested participants citizens, developer, and county staff. The 

specific role that earth-science data played in 

achieving this harmonious result is the subject of this 

chapter. The new plan itself, renamed "Lehigh," 

appears at the end of the chapter.

The Franconia area lies less than 10 miles southwest 

of the center of the District of Columbia. It is mainly 

a gently undulating, grassy upland capped by gravel 

and scarred by abandoned gravel pits. Its margins are 

incised by steeply sloping wooded ravines and gullies 

(see photograph right). The upland offers pleasant 

unobstructed vistas south and east across the Coastal 

Plain to the broad Potomac estuary and glimpses of 

the rolling wooded hills of the Piedmont area to the 

west.

The generalized current land-use map (upper map, 

opposite page) shows that most of the Franconia area 

is urbanized, some is low-density residential, and 

most of the undeveloped land is abandoned gravel 

pits. The northern part is crossed from east to west by 

the Capital Beltway Route 495, a limited-access

Aerial view looking northward across the vacant pitted upland and incised wooded

eastern margin of the Franconia area.

freeway, and the central part is crossed from north 

to south by the Richmond, Fredericksburg, and 

Potomac Railroad and by Interstate 95. Nearness to 

the Nation's fast-growing capital and relative ease of 

access makes the vacant land in the southeast part a 

prime target for residential development. Such a use 

is compatible with the comprehensive land-use plan 

for this part of Fairfax County (simplified on lower 

map, opposite page), provided that development is 

economically feasible without irreparable harm to 

potential homeowners or to the environment. The 

problem facing Fairfax County, then, was how best to 

help guide additional development in the Franconia

area and how to integrate it with the character and 

facilities of the surrounding region.

Several geologic conditions will affect development of this area. Because the upland area lies at the 

headwaters of three drainage basins, the probability 

of downstream flooding and siltation a common 

problem where urbanization increases the area of 

impervious surface will require a comprehensive 

storm-water management program. The area also has 

many slopes underlain by expansive clay that has a 

history of recurrent failure by landslide, slump, and 

creep. Even level terrain underlain by clay that shrinks 

and swells may have foundation-stability problems.

'New Franconia": development plan rejected in 1975

Mid - rise apartment

c- 0

Commercial /office

70
Generalized land-use map, Franconia area, 1974

Commercial, industrial, institutional

Transportation and utility corridors

Residential and parks (P)

Open space, undeveloped (U) and 

abandoned gravel pits (G)

2 MILES 

I

I

3 KILOMETERS

Commercial, industrial, institutional

Transportation and public services

Residential planned development units

2 MILES 

I

I

3 KILOMETERS

Simplified land-use plan, Franconia area

71
Development of the 

project

The issues

As viewed by the Fairfax County Office of 

Comprehensive Planning, the matters most relevant 

to further development of the Franconia area are:

1. Serving regional and countywide planning objectives 

such as planned development housing, environmental quality corridors 

(open-space system), and 

intracounty employment 

opportunities

2. Insuring compatibility with 

adjacent land uses

3. Making proper use of and 

upgrading existing transportation and public facilities

Earth-science information is especially useful for 

determining if space is adequate and appropriate for 

planned development housing; for providing data to 

help delineate environmental quality corridors, if 

present; and for identifying environmental or other 

physical constraints to transportation and public 

facilities.

Earth-science maps do not, of course, provide the 

total basis for the environmental aspects of land-use 

planning in Fairfax County; considerations such as air 

quality, noise, vegetation, wildlife habitats, and 

historical sites also bear on planning decisions. Even 

so, earth-science data provide the foundation upon 

which many other land-use aspects are based.

The planning process

A brief review of how environmental analysis and 

earth-science data fit into the Fairfax County planning 

process shows how earth-science maps are used in 

land-use planning decisions. The "critical path" a 

parcel of land follows with respect to planning, 

rezoning, and ultimate development is as follows:

1. Review of comprehensive 

regional and countywide 

plans.

2. Rezoning application by 

landowner.

3. Analysis (including environmental analysis) by Office 

of Comprehensive Planning and recommendation 

to Planning Commission.

4. Recommendation by .Planning Commission to County Board of Supervisors.

5. Approval or denial of rezoning by Board of Supervisors

6. Design review at site-planning scale.

7. Ultimate construction and 

development

Steps 1, 3, and 6 require thorough environmental 

baseline data, at different scales, to arrive at valid 

conclusions. For example, the environmental analysis 

done by the Office of Comprehensive Planning prior 

to recommendation for rezoning must determine 

whether the land is capable of supporting the use(s) 

proposed. Likewise, at the site-planning scale, 

information must be available to ascertain whether 

buildings, roads, sanitary sewers, water-supply facilities, and stormwater structures have been properly 

sited and designed, given the land and water 

characteristics of the site.

In the Franconia area, earth-science information 

has played a role at both levels of review and 

continues to affect modifications of the development 

plan.

PROCESS PRODUCT

INVENTORY

ANALYSIS

BASIC DATA

DERIVATIVE

AND 

INTERPRETIVE

SYNTHESIS

HW I IW I I I

I I 

Ift 

 Ml 

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CAPABILITY FOR PLANNED 

DEVELOPMENT HOUSING

ft HI (MM 

II I I 

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ftlftft 1 ' M

111

ftlftftftftftftftftftft

 till ftftftftftftl

 ft»«ftftftftftftftftftftftfttfftftWftI rtfttftftftftftftftftiftftftfttkftftftft i iIiiftft»«i11| i ftftfti

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 Mill!

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-HICAPABILITY

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Flow chart showing the use of earth-science data in the Franconia area

Using earth-science 

maps

Basic data maps of the Franconia area include 

topography, geology, and hydrology. They serve as 

sources for specific factors that are extracted to 

produce derivative maps. For example, the topographic map provides the information needed for the 

landforms map, which shows critical slope categories. 

Other derivative maps, such as the surface-materials 

map, can be combined with engineering data to 

provide information about relevant factors such as 

mineral resources or foundation conditions. By 

combining derivative maps, interpretive maps, such 

as slope stability, are generated. Finally, by combining 

derivative maps and selected basic data, a synthesis of 

information provides some possible solutions to landuse planning problems. The rest of this chapter

presents the basic and derivative maps used in review 

of the proposed development plan. 

The process starts with "inventory" (basic data maps), 

proceeds to "analysis" (derivative and interpretive 

maps), and then to "synthesis" (capability maps). 

In evaluating the Franconia proposal, computer 

processing was used to prepare composite maps and 

provide a rapid, inexpensive means of weighting 

variables and considering alternative solutions.

As part of the inventory process, planners consider 

not only the earth-science capability data but such 

other aspects as air quality, noise, wildlife habitats, 

and vegetation type to determine land-use suitability 

for the area. In turn, this environmental input is 

incorporated with such other factors as adjacent land 

use, economics, housing needs, transportation, and 

public facilities to reach final land-use recommendations.

72
^wyo ..' -..

Springfield

£ Springfield

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Springvale : : ..

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U^S COAST (it'ARD 

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STATION)

FOR BELVOIR

KESEKVAyiON

ROAD CLASSIFICATION 

Heavy-duty __^^_»_ Light-duty 

Medium-duty Unimproved dirt

Interstate Route T\ U. S. Route ( ) State Route

CONTOUR INTERVAL 10 FEET 

DATUM IS MEAN SEA LEVEL

ANNANDALE, VA.

N3845 W7707.5/7.5

1965

PHOTOREVISED 1971 

AMS 5561 1 SW-SERIES V834

Topographic map

The topographic map provides a wealth of 

information fundamental to land-use planning. In 

the Franconia area the topographic map (above) 

is accurate to the publication date, 1965, with photorevisions of cultural changes added in 1971. At the 

scale of 1:24,000 (1 inch=2,000 feet), it is the base on 

which all other map data have been compiled. It 

depicts the topography, the road and rail network, 

the densely urbanized areas, and the wooded 

parklands which constitute the framework within 

which development of the barren gravel pits and 

other undeveloped tracts must be harmoniously 

integrated.

Most of the proposed Lehigh development is 

outlined in the southeast (lower right) part of the 

map, and on all the maps that follow. The eastern and 

southern limits of the development go slightly 

beyond the map edges, so they have been omitted.

Topographic map showing the Franconia area

Proposed development outlined.

73
Landforms map

The landforms map (opposite page) is derived 

directly from the contours on the topographic map. 

The slope categories mapped, and illustrated on the 

sketch shown below, were selected by the Fairfax 

County Office of Comprehensive Planning to satisfy 

the greatest number of requirements for planning 

and for engineering design review. Delineation of 

slopes greater and less than 15 percent (about 81/2°) is 

needed to prepare a slope-stability map, as steeper 

slopes are less stable where underlain by most nearsurface materials.

The map shows planners at a glance, by color, 

where the steep slopes are that may prevent or 

constrain certain types of development. It also shows 

the broad, nearly flat upland and lowland areas where 

topography poses few constraints to transportation 

or construction.

Landforms in the Franconia area are intimately 

related to earth-shaping processes stream erosion 

and deposition being dominant in the lowlands, slow 

gravitational movement of earth materials most 

important on valley walls, and weathering in place 

most significant on the uplands.

Some landforms of the Franconia area: level uplands, in the foreground, 

descending by moderately sloping valley walls to gently sloping lowlands.

1. Lowlands - units 1a and 1b

2. Valley Walls - units 2c and 2d

3. Uplands - units 3a and 3b

Diagrammatic sketch illustrating landforms

LANDFORM UNIT SLOPES DESCRIPTION

Lowlands

Less than 3 percent Nearly level flood plains of major streams; underlain by alluvium and subject 

to periodic flooding of varying intensity

Less than 8 percent Gently sloping plains; locally underlain by alluvium and subject to flooding 

by major storms

Valley Walls

r 

ft

2c 8 to 15 percent Moderately sloping valley walls; transitional between valley flood plains and 

the adjacent uplands

15 percent or more Includes the steeper valley walls, with slopes generally 15-30 percent, with 

maximum of 40 percent

74
SCALE 1:24000

1 MILE

1 KILOMETER

Landforms map, Franconia area

From Rogers (1975)

LANDFORM UNIT SLOPES DESCRIPTION

Uplands

Less than 3 percent

3 to 8 percent

8 to 15 percent

Nearly level upland: broad open terrain, marked by gravel pits; dissected by 

streams that have flat-bottom valleys

Undulating upland, dissected by streams that have cut deep valleys of varying 

width

Rolling to hilly upland, with locally steep slopes (not shown on sketch)

75
Geologic map

The geologic map of the Franconia area (opposite 

page) shows the distribution of earth materials. 

Although the terms and symbols are generally 

familiar only to earth scientists, the map provides the 

factual background needed for further environmental analysis and for preparation of the derivative 

and interpretive maps more directly usable by 

planners. Hard crystalline metamorphic and igneous 

rocks (Gr, Wm, Wd) are exposed along Accotink 

Creek, and soft red-brown saprolite (Grs, Wms, Wds) 

occurs at the surface in the northwestern and western 

part of the area. (Saprolite is a porous clay-rich 

residual material, formed by chemical weathering of 

crystalline bedrock in which the structure of the 

original rock is preserved.)

Saprolite is overlain by poorly consolidated much 

younger sediments of the Coastal Plain along the Fall 

Line, an imaginary line formed by joining the low falls 

or rapids of major streams that form a barrier to 

navigation at the boundary between the soft younger 

rocks of the Coastal Plain and the harder rocks of the 

Piedmont. In the Franconia area, the Coastal Plain 

deposits consist of a wedge of sediments that thickens 

to the east. Beds or layers of sediment within this 

wedge are inclined, or dip, gently to the southeast, 

parallel to the slope of the base of saprolite, as shown 

on the simplified geologic cross-section A-B (below) 

and the geologic sketch (right). These sediments have 

been subdivided into two units, one mainly sand

FALL LINE

DH 1: Drill hole penetrating upland 

gravel and entering Kps

DH 2: Drill hole penetrating upland 

gravel and entering Kpc

Symbols are as 

shown on explanation 

of geologic map

Geologic sketch of Franconia area

with scattered quartz and clay pebbles (Kps), the 

other mainly silty or sandy clay (Kpc). Each unit grades 

laterally into the other, the sand unit containing 

interbeds of sandy clay and the clay unit containing 

thin interbeds of sand (see photograph below).

Younger upland gravels (Ugl) overlap the Coastal 

Plain sediments and rest directly on saprolite in the 

western part of the Franconia area. The upland 

gravels blanket the surface, forming the top of the

plateau. Underlying units are exposed mainly along 

ravine and gully sides.

Terrace gravels (Qt) that locally include thin 

colluvium or deposits of slopewash (Q/Tc) border 

deposits of stream valley alluvium (Qal). Disturbed 

ground (Dg) and fine-grained sediment pond fill (As) 

occur near abandoned gravel pits, and artificial fill 

(Af) is present in low areas along railroads and 

highways.

VERTICAL EXAGGERATION X 8

Simplified geologic cross section along line A-B, Franconia area

Coastal Plain sediments in the Franconia area, consisting of interbedded sand (light color) and clay.

76
SCALE 1:24000

o

From Huffman, Froelich, and Force (1975)

1 MILE

1 KILOMETER

Geologic map of Franconia area

Q/Tc-colluvium

(Quaternary and (or)

Tertiary)

COASTAL PLAIN 

DEPOSITS

SEDIMENTARY ROCKS

Terrace deposits (Quaternary)

ARTIFICIALLY CHANGED GROUND

Sediment pond fill

Upland gravel (Quaternary)

Potomac Group

(Cretaceous) 

Kps - sand and gravel 

Kpc - clay and silt

Disturbed ground

METAMORPHIC AND IGNEOUS ROCKS 

(Precambrian and (or) Lower Paleozoic)

Grs

Gr

Gr - granitoid rocks (Clarendon

granite, Occoquan granite,aplite, 

pegmatite, quartz diorite, etc.)

Grs - saprolite on granitoid rocks

Wms

Wm

Wissahickon Formation 

Wm - metagraywacke 

Wms - saprolite on metagraywacke

Wds

Wd

Wd - diamictite gneiss 

Wds - saprolite on

diamictite gneiss J

PIEDMONT 

ROCKS

Contact, approximately located

70

Strike and dip of predominant foliation 

Strike of vertical foliation

70

Strike and dip of predominant joint set 

Strike of vertical joint set

Gravel pit

-B

Cross section on 

opposite page

77
Surface materials map

The surface materials map (opposite page) is 

derived mainly from the geologic map but also 

incorporates relevant soils data. Definition of map 

units is based largely on their engineering characteristics (see table below). For example, different 

geologic units such as Occoquan Granite and Wissahickon Formation are grouped together as unit 7, 

bedrock, because their engineering properties are 

similar to one another but are very different from 

other surface units. By using the surface materials 

map and accompanying table in conjunction with 

additional field observations, other maps can be 

derived that deal with specific properties applicable 

to solving many different problems.

FALL LINE

DH 1: Drill hole penetrating upland 

gravel and entering Kps

DH 2: Drill hole penetrating upland 

gravel and entering Kpc

Symbols are as 

shown on explanation 

of geologic map

SURFACE MATERIALS

Geologic sketch of the Franconia area, 

emphasizing the surface materials

The wedge edge of Coastal Plain sediments 

overlies saprolite formed on much older 

gneiss and granite and underlies much 

younger upland gravels. The upland 

gravels have been dug as a source of sand 

and gravel, and the granite is locally 

quarried as crushed stone. Soils on the 

upland gravel locally contain a shallow 

hardpan which impedes downward percolation of rainwater and locally protects 

the swelling clay from moisture.

Soils and 

upland gravel 

Clayey silt loam (Csl)

(with hardpan, poorly drained) 

Sandy silt loam (Scl) 

(well drained)

Saprolite (Granite-Grs, Gneiss-Wds) 

Clay and silt (Kpc)

Sand and gravel (Kps) 

(ch indicates possible 

channel-fill sands)

Granite (Gr)

Foliated Wissahickon Gneiss (Wd)

An example of a specific properties map would be 

one of potential mineral resources in the Franconia 

area that might show only the available surface 

sources of sand and gravel (unit 4), sand (unit 5b), 

crushed stone or building stone (unit 7); or a map 

showing shallow foundation conditions in the Franconia area that might define saturated alluvium 

(unit 2) as "low strength," sand and gravel (units 4and 

5b) as "moderate strength," and bedrock (unit 7) as 

"high strength" (see table right).

Soil characteristics can be incorporated into this 

map, particularly by means of the columns on unified 

soil classification and "permeability." A derivative 

map of surface drainage and infiltration characteristics might classify "poorly drained soils" as those 

found on units 1, 2, 4, 5a, and 7, "well-drained soils" 

on units 3 and 5b, and "fairly well-drained soils" on 

units 6b, 6c, and 6e.

Planners frequently need information related to 

road construction and slope stability, which can be 

major development cost items. The unified soil 

classification column is a useful indicator of the soil 

support characteristics for city streets. Slope-stability 

characteristics of fine-grained soils during construction can be estimated from the strength properties 

column. The strength properties column can also be 

used by engineers to estimate which units are 

adequate for deep foundations where piles are 

needed.

Characteristics of surface

Map 

symbol

1 

2

Name of unit 

(symbol on 

geologic map)

Artificially changed 

ground: 

Af ......................

Alluvium (Qal) ......

Topographic form and mode of occurrence

cross streams and saddles; extensions of flat land 

for buildings.

plants.

... Nearly level plains along streams.

Maximum 

thickness 

(feet)

50

30

20 

50

Unified soil 

classification1

Variable ...................

CH, CL ....................

Variable ...................

SW, SP, SM, CW, 

CP, CL, OL

"Permeability"2

Cood to fair .............

Ease of excavation

Easily moved with heavy 

power equipment.

do..

.................... do ........................

..................... do ........................

5b

Terraces and Nearly level plains. Terraces are river deposits;

colluvium colluvium includes slump and creep deposits

(Qt, Q/Tc). on slopes, lag gravel on flat uplands.

Upland gravel Extensive flat plateaus with eroded borders.

(Ugl) Sheetlike deposits of gravel and sand.

Clay and silt (Kpc) Cently southeast sloping surface locally dissected 

Unconsolidated by modern streams; outcrops in steep sides of 

sand and clay valleys and scarps between upland and lowland 

(Kpc) surfaces; former river channel and flood-plain 

deposits; may be deltaic in part.

Sand and gravel ........................................ do

(Kps)

30 CP, CM, SP, SM, 

ML, CL

30-50 CP, CM, SP, SM, 

ML, CL

Excessive to poor. .... ...................... do -

Excessive to good ex- .......................do .

cept through hardpan; hardpan may 

change seasonally.

CL, CH, SC .............. Poor

SW, SM, SC, CM

Easy to moderately difficult 

with heavy power equipment, depending on soil 

stiffness.

Cood ........................... Easy with heavy power

equipment.

6b

6c

Saprolite:

Crs ........................

outcrop 

(Wd, Wm, Cr).

valleys. Saprolite (weathered rock) more than 

10 feet thick on various fresh crystalline bedrock 

types.

smaller stream banks. Fresh bedrock with less 

than 10 feet of overburden.

Easy to moderately difficult

with heavy power equipment, depending on 

hardness.

....... ...................... do .......................

. . ..do.......................

blasting.

78
< " '</^^%%W<>*...^ : ^f^s,u r^

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From Force and Froelich (1975)

materials, Franconia area

Strength properties3

 Allowable footing loads 

Fine grained Coarse grained [tons per square foot (TSF)] Remarks

Medium ................ Medium ................. To 1.5 TSF; low to moderate.

Very soft ................ ................................ None .................................................._........ Includes swelling clay.

Very soft to medium. Loose to medium. None to 1.5 TSF; none to moderate .... Changes natural drainage.

............ do.............. .............do.............. None for organic silt and clay to 2 TSF Subject to recurrent flooding; usually

for coarse-grained soils; allowable saturated, 

loads generally low.

Soft to medium.

Medium to very 

stiff.

Medium to 

extremely stiff.

Loose to compact. Less than 1 TSF for fine-grained soils, 

1.5-3 TSF for coarse-grained soils; 

allowable loads generally low to 

moderate.

...............do................ 0.5-3 TSF for fine-grained soils,

1.5-4 TSF for coarse-grained soils; 

allowable loads generally moderate 

to high.

1-5 for plastic clay,4 4-7 TSF for 

sandy clay; allowable loads 

generally moderate to high.

Medium to very 

compact.

Medium to Loose to very

extremely stiff. compact. 

(Joints may be filled with weak soi I or clay)

May be saturated at base. Can be used as 

aggregate if fresh and sized.

Removing hardpan may permit water to 

enter underlying swelling clay (5a). 

Can be used as aggregate if fresh and 

sized. Color usually red, brown, or 

yellowish brown (matrix).

Includes much swelling clay which expands when wet, shrinks when dry; 

landslide prone; tends to crack foundations. Some clay may be used for 

lining retention ponds. Unweathered 

color: light gray to light olive gray; 

weathered: reddish brown.

Porous; readily absorbs surface water; 

potential infiltration ponds where 

properly engineered. Potential aquifer. 

Aggregate for concrete where fresh and 

washed. Unweathered color: light gray; 

weathered: brown, reddish brown, 

yellowish brown.

1.5 TSF at ground surface to 5 TSF at Used as fill, difficult to compact owing to 

depth where rock fabric is retained; high mica content. Significant quanallowable loads moderate to high. tities of ground water in porous,

relatively permeable units.

5-6 TSF; allowable loads generally high.

(Compressive 

strength range, 

5,000-15,000 

Ib/in2)

10-60 TSF; allowable loads very high.

Do.

Can be crushed for use as aggregate; 

granite formerly quarried. Generally 

poor as road metal owing to rapid 

weathering characteristics. Some ground 

water available in fractures and joints.

Footnotes to table:

'Unified soil classification of Corps of Engineers 1953-57:

[Sequence of symbols in opposite table indicates relative abundance]

Major division

Group 

symbol Soil description

Coarse grained Gravelly soils (over 

(over 50 percent half of coarse 

by weight coarser fraction larger 

than No. 200 than No. 4 

sieve). seive).

Sandy soils (over 

half of coarse 

fraction finer 

than No. 4 

sieve).

Fine grained Low 

(over 50 percent compressibility, 

by weight finer 

than No. 200 

sieve).

High 

compressibility.

GW Well-graded gravels, sandy gravels. 

GP Gap-graded or uniform gravels, sandy

gravels.

GM Silty gravels, silty sandy gravels. 

GC Clayey gravels, clayey sandy gravels.

SW Well-graded sands, gravelly sands.

SP Gap-graded or uniform sands, gravelly

sands.

SM Silty sands, silty gravelly sands. 

SC Clayey sands, clayey gravelly sands.

ML Silts, very fine sands, silty or clayey fine

sands, micaceous silts.

CL Low plasticity clays, sandy or silty clays. 

OL Organic silts and clays of low plasticity.

MH Micaceous silts, diatomaceous silts, volcanic ash. 

CH Highly plastic clays and sandy clays.

^Permeability is the quality of a soil that enables it to transmit water and air; in this table, 

the term refers to percolation rates in septic tank drain fields.

Consistency and compactness scales: 

Fine-grained soils

Silt and clay consistency

Unconfined com- Coarse-grained soils, sand, 

pressive strength (TSF) and gravel compactness

Very soft ..........

Soft ..................

Medium ..........

Stiff ..................

Very stiff ..........

Extremely stiff

0.25

0.25-0.5

0.5-1.0

1.0-2.0

2.0-4.0

4.0

Very loose

Loose

Medium compact

Compact

Very compact

4The swelling potential of highly plastic clays must also be considered in engineering 

design.

Surface materials map, 

Franconia area

Colluvium and terrace gravel

Sand and gravel

'eh

1

6c 6e

Saprolite

Bedrock

79
Subcrop map

The subcrop map (opposite page) shows the 

subsurface material that lies directly beneath the 

surface materials units of the upland. If the soils, the 

entire upland gravel deposit, and the fill in abandoned pits could be peeled away, as sketched at 

right, the saprolite, clay, and sand units beneath them 

would appear as shown on the subcrop map. This is 

also illustrated by the photograph below.

The chief purpose of the map is to show the 

distribution of impermeable clay, which is critical to 

evaluating infiltration and shallow drainage characteristics. Another use for the map is to help assess the 

general deep foundation conditions, where piles and 

caissons must be used, by matching the subcrop unit 

with the column on strength properties (see table on 

surface materials) relating to bearing strength. Information for specific sites., of course, would require 

engineering studies at a much more detailed scale.

Geologic sketch of the Franconia area,

emphasizing subcrop materials

beneath the soil and gravel cover

The wedge edge of the Coastal Plain 

sediments overlies saprolite formed on 

much older gneiss and granite and underlies much younger upland gravels. The 

Coastal Plain rocks consist ofinterfingering 

sand and silty clay beds which were deposited by rivers. The sand may fill old 

channels and the clay and silt may be overbank floodplain deposits, natural levees, 

oxbow deposits, and possibly deltaic. 

Under certain conditions the sand acts 

as an aquifer for ground water, whereas 

the clay, which swells when wet and is 

slide prone, forms confining beds.

Symbols are as 

shown on explanation 

of geologic map

SE

SURFACE MATERIALS

FALL LINE

DH 1: Drill hole penetrating upland 

gravel and entering Kps

DH 2: Drill hole penetrating upland 

gravel and entering Kpc

Soils and 

upland gravel 

Clayey silt loam (Csl)

(with hardpan, poorly drained) 

Sandy silt loam (Scl) 

(well drained)

Saprolite (Granite-Grs, Gneiss-Wds) 

Clay and silt (Kpc)

Sand and gravel (Kps) 

(ch indicates possible 

channel-fill sands)

Granite (Gr)

Foliated Wissahickon Gneiss (Wd)

3<. '*^ff

,W- ^ftt«.T >'. v-*" »-*.<*.* -.

' tp.,i..-'^'*«S - ,Jk' ;^**te'-^.: '-&i 

^ ._. a . ., -w-v- -- -» , -<-',TrJ>^^'J^>ir^S?Sw

Crossbedded sand beds beneath gravel cover.

80
^ /^yS^^^.jft^

SCALE 1:24000

o 1 MILE

1 KILOMETER

Subcrop map, Franconia area

Clay beneath upland gravel (4) or fill (1)

Sand beneath upland gravel (4) or fill (1)

Saprolite beneath upland gravel (4) or fill (1)

81
Slope-stability map

The slope-stability map (opposite page) shows the 

distribution of materials of different relative slope 

stabilities in four categories: high, moderately high, 

moderately low, and low. These categories indicate 

the relative possibility of future problems both in 

natural slopes and in manmade cuts. The relative 

stability is determined by combining the landforms 

map (p. 75) that includes slope categories with the 

surface-materials map (p. 79) and the related table, 

as different materials are stable at different slopes. 

Information for specific sites naturally requires much 

more detailed engineering studies.

Areas of high stability are generally level or slope 

gently regardless of the type of underlying material, 

or slope moderately but are underlain by strong 

material such as bedrock.

Areas of moderately high stability generally include 

clay on gentle slopes, sand on moderate slopes, and 

saprolite and bedrock on steep slopes. Failures in the 

bedrock are likely to be in the form of rockfalls, and 

failures in the saprolite will probably be controlled by 

joints or foliation. Failures in clay and sand will 

probably be by local slumps or creep, except where 

gentle slopes are oversteepened by construction.

Areas of moderately low stability are either sand on 

steep slopes or clay on moderate slopes. Naturally 

occurring slumps and progressive failure by creep are 

common in this category.

Areas of low stability, which are extensive in this 

region, are those where clay occurs on steep slopes. 

Naturally occurring slumps, both recent and old, 

cover a significant part of such areas.

Small landslides are shallow, perhaps not more than 

5 feet deep. Larger landslides, more than about 100 

feet long from the top to the toe of the slide, may be as 

much as 30 feet deep. Large landslides in the 

Franconia area are of three types: rotational slumps, 

planar glide blocks, and combinations of these two. 

Rotational slumps and planar glide blocks are shown 

in the diagrams at right.

In some parts of the Franconia area, the toes of 

large slumps have moved hundreds of feet, as though 

the soil had been nearly liquefied. Two glide blocks 

have moved downslope more than 400 feet, and many 

others have moved 200 feet or more. Most such landslide deposits consist of weak, fractured material that 

could be reactivated. Reactivation can be caused by 

removal of the toe, overloading the crown, or by 

blockage of natural ground-water seepage.

Almost all moderate and steep slopes on clay show 

evidence that surface materials have slowly moved 

downslope. Disturbing these slopes further by 

construction may cause renewed movement, acceleration of soil creep, or induce new slides.

TOP

ORIGINAL GROUND 

SURFACE

Ugl

TRANSVERSE 

RIDGES

RADIAL 

CRACKS

Rotational slump

Diagrams modified 

from Varnes (1958)

Planar glide block

Franconia area landslide types

Rotational slumps consist of highly disturbed mixtures of materials; they are 

characterized by a scarp at the top of the 

slide, by transverse cracks and ridges, and 

radial cracks and hummocky ground at 

the toe. The surface of rupture is arcuate 

in cross section. This type of landslide is 

commonly present in the Kpc unit, and in 

Kpc capped by the Ugl unit.

Planar glide blocks are slides composed 

of essentially intact material that moved in 

the manner of a block sliding down a 

plane. Planar glide blocks may be evidenced by the displaced topographic 

position of Ugl and are commonly underlain by the Kpc unit. Numerous planar 

glide blocks are present on the steep 

slopes near Dogue Creek.

Typical landslides on steep slopes underlain by clay in the Franconia area.

82
«-: / <rf i,- -^ r%*?

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B0erly ' 

Foresjt :...

SCALE 1:24000 

o 1 MILE

1 5 0

I I l i l l I l l l F=

1 KILOMETER

Slope-stability map, Franconia area

RELATIVE SLOPE 

STABILITY

SURFACE MATERIAL 

UNIT

GEOLOGIC MAP 

SYMBOL

LANDFORM 

UNIT 1

Low

Moderately 

low

Moderately 

high

5a (Clay)

5a (Clay) 

5b(Sand)

1 (Fill) 

3 (Gravel) 

5a (Clay) 

5b(Sand)

6 (Saprolite)

7 (Bedrock)

Kpc

Kpc 

Kps

Dg,Af

Qt, Q/Tc

Kpc

Kps

Wds. Wms, Grs

Wd, Wm, Gr

2d

2c,3c 

2d

2d

2c, 2d

1b,3b

2c,3c

2d

2d

High All other combinations of surface material units and 

landform units

1

Slopes associated with different landform 

map units are as follows:

1a, less than 3 percent

1b, 3 to 8 percent

2c, 8 to 15 percent

2d, greater than 15 percent

3a, less than 3 percent

3b, 3 to 8 percent

3c, 8 to 15 percent

Note: Although an area is designated as being in a relatively 

low stability category, engineering studies at a given 

site may establish that the site is suitable for homes 

or other types of construction activity.

83
Hydrologic map

The hydrologic map (opposite page) provides 

information on surface water for land-use planning in 

the Franconia area. The map shows the drainage net 

and flood-prone areas the chief hydrologic conditions that have influenced the development patterns 

and construction plans in the Franconia area. Several 

aspects of ground water are significant for planning, 

but unfortunately the available data are insufficient 

for confident use.

The drainage net shows the location of drainage 

divides, ponds, streams, and gullies. The net is 

obtained directly from the topographic map, with 

additional data interpreted from contours that 

indicate the shape of the eroded land surface sloping 

toward perennial streams. The inferred surface 

drainage in shallow gullies shows the probable 

avenues of overland flow.

Nearly all the proposed development lies in the 

headwaters of Dogue Creek and several of its tributaries. Development here is likely to aggravate 

downstream flooding and deposition of silt. This 

is a common problem wherever urbanization increases the area of impervious surface.

Flood-prone areas shown on the map have a 1-in100 chance on the average of being inundated during 

any year. The flood boundaries have been estimated 

from regional relations between stream stage and 

flood frequency. A county ordinance specifically 

prohibits any construction within or unauthorized 

alteration of the 100-year flood plain.

Another county ordinance prohibits new developments from increasing peak overland runoff that 

may result in increased downstream erosion, sedimentation, and flooding. To insure that storm-water 

runoff will not cause such adverse effects downstream, excess storm water has been managed in the 

Franconia area by means of onsite retention ponds, 

or onsite recharge or infiltration pits that permit 

the collected runoff to percolate downward to the 

water table. Either of these methods will reduce 

peak runoff, as shown on the hypothetical hydrograph at right. Recharge pits can be constructed at 

any site where porous sand (Kps) extends from the 

bottom of the pit to the water table. To function best, 

a recharge site should have a depth to the water table 

of more than 10 feet to allow for excavation. (Only 

onsite retention ponds are considered here, because 

the feasibility of using recharge pits involves a 

complicated determination of the depth to the 

water table and evaluation of the near-surface 

thickness and permeability of sand.)

Retention ponds can be constructed at any site 

where clay beds impede the downward movement of 

water. Overlaying the distribution of clay (Kpc, 5a) 

shown on the surface-materials map (p. 79) with the 

gravel on the subcrop map (p. 81) and on the drainage 

net defines the potential sites for surface retention 

ponds. Shallow test borings and percolation tests are 

needed to confirm the capability of any site selected 

as a possible retention pond. Using natural surface 

runoff channels to drain storm water from paved 

areas to retention ponds makes it possible to manage 

natural storm waters with less adverse downstream 

impact. Ultimate disposal may be by both evapotranspiration and controlled discharge.

Temporary storage of runoff in 

retention pond

Direct runoff from 

impervious area via 

storm drain Retention 

pond

Natural vegetation

Hypothetical hydrograph showing reduction of flood peak resulting 

from use of retention ponds, Franconia area

Typical retention pond designed to reduce 

flood peaks.

84
_ S COAST (J 

 .,*-' "' Rt

SCALE 1:24000 

o 1 MILE

1 KILOMETER

Hydrologic map, Franconia area

^^/

100-year flood limit Drainage divide

Perennial drainage Surface impoundments

Intermittent drainage

?

Springs

85
Capability map for

planned development

housing

In considering the Lehigh proposal, the constraints 

posed by the existing environment were taken into 

account, as were the effects on the environment 

which are likely to follow. The constraints are 

illustrated by the slope-stability problem: Construction on unstable slopes will be subject to damage 

from slope movement. Likely future environmental 

effects are illustrated by the probability of increased 

frequency and severity of flooding resulting from 

increased runoff from built-over surfaces. The earthscience factors that require consideration to insure 

sensitive planning and development are listed in the 

table below; associated with each factor are related 

problems and suggestions. All of these factors have 

entered into preparation of the capability map for 

planned development housing (opposite page). As a 

synthesis of the earth-science data and interpretations relevant to development in general, the map 

was used by the county planners to make substantive 

recommendations and proposals bearing on the 

proposed Lehigh development.

Because of the number of factors involved, the 

synthesis was carried out by computer composite 

mapping. This mapping technique is demonstrated 

by a hypothetical example (right). For the Franconia 

area, the computer stored the data in the form of 

three factor maps (above right) which in turn yielded 

the composite capability map.

In the computer composite map (opposite), the 

lighter toned areas are the more favorable for 

planned housing. Favorable areas are on the upland 

in zones of moderately high and high slope stability 

that are underlain by gravel and sand. Potential sites 

for storm-water retention ponds are shown in lowlying areas which are underlain by clay.

Using these earth-science considerations as a base, 

the other environmental factors mentioned previously wildlife habitats, air quality, noise, vegetation type are then brought to bear to determine 

optimal land use for the area. In turn, land-use 

planners weigh this environmental input with such 

other factors as adjacent land use, economics, housing needs, transportation adequacy, and public 

facilities to arrive at final land-use recommendations.

Earth-science factors, attendant problems, and suggestions, 

Franconia area

Earth-science factors Problems Suggestions

Expansive clay on 

slopes >15 

percent.

Expansive clay on 

slopes <15 percent or beneath 

abandoned pits 

or upland gravel.

Variable distribution of sand and 

clay layers beneath upland 

gravel or fill.

Distribution of 

expansive clay.

Slope instability

Foundation instability; drainage 

problems.

Low-density development; retain 

as wooded area. Engineering 

geologic site studies required.

Engineering study for all structures; use as retention ponds.

Inconsistent, Cluster units on best available 

variable strength upland sites, based on drilling 

properties. program to minimize construction on expansive clay.

Retain water onsite using natural 

catchment areas underlain by 

expansive clays as retention 

ponds. Design foundations for 

swelling conditions.

Distribution of 

flood-prone 

areas, alluvial 

soils, and steep 

slopes.

Complicates 

storm-water 

runoff collection 

and retention; 

unstable foundations for surface 

structures.

Flood hazard, Retain areas as environmental 

high-water table, quality corridor and park lands; 

low-strength integrate with storm-water 

properties. runoff program.

Subcrop map showing distribution of clay 

beneath the gravel cap

CLAY DRAINAGE

STEEP 

SLOPES

SOURCE MAPS

It!

DIGITIZED MAPS

VALUE

0

0

0

1

1

1

0

0

1

SCORES

4

0

2

7

3

1

4

4

1

COMPUTER

COMPOSITE

MAP

| | no factors present 

Q] day 

\/\ drainage

clay and drainage

unstable slopes

day, drainage, and unstable slopes

Computer composite mapping technique for a hypothetical area

Source maps are divided into cells of a 

preselected size (a) and map units are 

stored as numeric codes, represented d/'agrammatically by shading (b). Weighted 

numeric values are assigned to the digitized map units, based on their relative

importance (c), and the computer sums 

these values to produce a "score" for each 

cell (d). The composite map (e) is produced 

on a computer line printer, with a different 

symbol to represent each score, or combination of factors.

86
1 :::;::::::::::::::::::::::::::::: 

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Hydrologic map showing location of natural 

drainageways and surface water

Slope-stability map showing distribution 

of unstable slopes

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Scale 1:24,000

WWW Developed areas

XXX 

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special engineering studies required

 » » Potential retention pond sites

I I I Favorable areas for planned development housing

999

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Multiscale data analysis and mapping program 

by Glenn H. Beavers, for Land Use Analysis Laboratory 

and Agricultural and Home Economics Experiment 

Station. Iowa State University

87
Conclusion

Earth-science data used in the inventory-analysissynthesis process provide the foundation on which 

land-use planners and developers can plan, design, 

and build in a manner harmonious with and sensitive 

to the natural environment. In Fairfax County such 

data will also provide the basis for formulating and 

implementing new ordinances and strengthening 

existing ordinances related to significant earthscience factors. The computer-assisted preparation of 

a capability map illustrates how the complex 

interrelations between the natural environment and 

man's use of the land can be dealt with in an 

objective, consistent, and time-saving manner.

In the Franconia area, earth-science information 

has significantly influenced the decisions related to 

the rezoning application for planned development 

housing. At the two levels of the Fairfax County 

planning process where environmental analysis 

occurs rezoning application review and development plan approval these data and related interpretive maps were critically important for determining appropriate land uses and subsequently 

modifying the detailed development plan. The slopestability map identified areas on which development 

is now discouraged; the gravel subcrop map defined 

areas with potential foundation and drainage 

problems. The hydrologic analysis provided a lowcost alternative using natural drainageways for 

managing increased storm-water runoff. The resulting environmental quality corridor is interconnected 

throughout, with stream valleys joined by wooded 

areas on hazardous slopes. These objectives were 

attained while retaining the density requested by the 

developer and approved by the county. Thus, the 

Lehigh plan takes far greater account of the natural 

setting and processes than did the "New Franconia" 

plan.

"New Franconia": 

proposed development disapproved in 1975

 -I- . /' " _-..' " xV* ' '/' ' .' '' *Cf-Xq,\

v'/ . />^ S\J ^

ravel' i ¥ .' ."- p<t". * *' >.." * . 

-k. ' -*..-* i' " " «- ' *. *

~r ./:-'. ' -N^V

38°45'

77°07'30"

Townhouse construction in Fairfax County

The single-family attached residences 

of Lehigh will probably be similar

88
Single - family detached

Lehigh development plan, approved in 1976

In this plan, the original submission (shown 

on opposite page) is modified in both mix 

and distribution of housing types. Unstable 

slope conditions, also on the map below 

and noted in the county's rezoning application review, necessitated a more dense 

cluster form of development from the 

standpoint of both environmental sensitivity and economic feasibility. Although 

several development areas still include 

potentially unstable slopes, special precautions will be taken during construction 

to prevent slope failure and to avoid 

subsequent damage to structures.

Low - rise apartment 

I MRA ]

Mid - rise apartment

Potentially unstable slope

SCALE 1:24000

1 MILE

1 KILOMETER

38°45

77°07'30"

Communities in Fairfax County

The single-family homes of 

Lehigh will likely resemble them.

89
Closing thoughts

By G. D. Robinson and Andrew M. Spieker

We presented our samples from west to east. This 

is not only a natural reading order, from left to right, 

but also an order of increasing complexity: from 

such comparatively simple applications as regulating 

setback of buildings on eroding seacliffs, requiring 

only a few earth-science maps, to the much more 

difficult application of new town planning, requiring 

many. In this way, we hope to have demonstrated the 

planning and decisionmaking value of earth-science 

maps without wholly exhausting our readers.

The sample has been, we think, sufficient for its 

illustrative purpose, but it is only a sample. It ignores 

most of the country, and in so doing it also neglects 

some common geologic settings and touches lightly 

if at all on some major planning problems involving 

earth science. Thus there are no examples of application in areas underlain by thick and continuous 

glacial deposits, such as prevail in much of the 

northern Middle West; or examples in areas underlain by natural caves in limestone, widespread in the 

Southeast; or in areas underlain by igneous rocks, 

common in the Northwest and Hawaii. The use of 

underground space and the management of wastes 

(which often coincide), two topics of major and 

rapidly expanding proportions, are treated only 

briefly.

Much has been published or is available in file form 

about these and other geographic and topical areas, 

far more than we could cite individually. Readers 

can learn what is available by communicating with 

the appropriate State geological survey or U.S. 

Geological Survey office (listed on p. 91-92) or the 

earth-science departments of nearby colleges or 

universities. A few references to some neglected 

major applications are included in the list of suggested reading that follows.

Readers should be aware that their chances of 

finding all the earth-science maps they need are 

only fair. Topographic maps or orthophotoquads are 

almost universally available for urban and urbanizing 

areas, and flood-prone area maps can be had for most 

areas commonly subject to flooding, but the same 

cannot be said for geologic maps or for maps pertaining to ground water. It follows, then, that interpretive maps, like the many in this book, that translate 

earth-science information into forms and terms useful to planners and managers are even less widely 

available. Further, as noted in the "Introduction," 

little new mapping is being added in urban areas 

because the earth-science profession has not been 

directed to do more. Significant increase in the

capability of the earth sciences to produce more 

information for better land use decision awaits 

increased demand by present and potential users.

"Land management," "water management," and 

"land-use planning" are emotion-filled terms, touching as they do on some of the deepest and most 

contradictory aspects of human nature. A significant 

decision involving land or water, whether made by 

owner, developer, or government entity, has probably never been happily accepted by everyone 

affected. Somebody always loses, or thinks he has 

lost. Indeed, the fear of possible loss often permeates 

the atmosphere of significant decisions from the very 

beginning, so that the geologic and hydrologic facts 

of the situation, and their likely consequences, may 

be ignored or never ascertained. With increasing

frequency, this neglect is made apparent in legal and 

political contests of land and water decisions.

The main message of this book is that more sensible 

and defensible if never universally popular land 

and water decisions will be made if all relevant earthscience information is assembled and applied throughout the planning and decisionmaking process.

We are all planners and decisionmakers. Anyone 

who changes the use of a bit of the Earth, if only to 

build a house or drill a well to irrigate a garden, is 

both. It is in his own long-term interest, as well as 

that of the community, to plan and manage his 

"development" in accord with the natural limitations 

and opportunities offered by the setting. Not to do 

so is to court waste, damage, sometimes even injury 

and death.

Engineers Testing Laboratories, 1960

'...and we can save 700 lira by not taking soil tests."

Acknowledgments

This book is an outgrowth of an idea put forth 

several years ago by John D'Agostino, to produce a 

comprehensive guide to the use of earth-science 

maps for users who are not earth scientists. Such a 

comprehensive work was not yet feasible, but the 

present more limited venture has profited greatly 

from D'Agostino's experience and ideas.

The editors are deeply indebted to the authors who 

interrupted their busy lives to produce the various 

chapters, and especially to the non-Survey authors, 

who did so with token compensation or none. We 

are also grateful for the cooperation and understanding of their supervisors.

The authors of two chapters in turn wish to acknowledge special assistance from associates outside the

90

Geological Survey. Donald A. Woolfe, Planning 

Director, San Mateo County, explained the role 

played by earth-science information in that county's 

planning process, and Anne A. Parke, Planner, San 

Mateo County, reviewed the Central San Mateo 

County chapter. Much information for the Tucson, 

Arizona, chapter was provided by Alex R. Garcia, 

Director of the Pima County Planning Department, 

and the chapter was reviewed by Lance McVittie and 

Robert C. Johnson, Pima County Planning Department; by Frank Brooks, former Director, Tucson 

Water Department; and by Kirk Guild and Walter 

Stein, City of Tucson Water Production Department.

Throughout the report, illustrations not specifically 

credited were prepared by the authors of the respective chapters.

Finally, the authors and editors are indebted to 

scores of associates for assistance in all aspects of 

this rather unusual book. As it is hopeless to acknowledge the contributions of all, and impossible not to 

overlook some, we will note only extraordinary

contributions from within. Vincent E. McKelvey, 

who was Director of the Geological Survey while 

the book was being written and made ready for the 

press, vigorously encouraged its preparation and 

reviewed the manuscript in detail, offering many 

productive suggestions. Paul Y. W. Ho and Jeffrey A. 

Troll were largely responsible for the design of the 

book, and Ho created most of the art work. The cover 

is the work of James L Caldwell. Helpful reviews of 

the entire manuscript were made by Robert D. 

Brown, Jr., Rachel Barker, and Donald R. Nichols, 

geologists; John H. Feth, L. A. Heindl, and Eugene 

R. Hampton, hydrologists; Gerald Greenberg, 

geographer; William J. Kockelman, planner (all 

of the Geological Survey). Constructive reviews 

were also made by Kurt W. Bauer, Planner and Executive Director, Southeastern Wisconsin Regional 

Planning Commission, and by Professor James E. 

Hackett, geologist, College of Architecture and 

Urban Studies, Virginia Polytechnic Institute and 

State University.
Sources

Listed below are sources of two kinds: first, places 

to go for earth-science information; second, references. The references, in turn, are of two sorts: first,

suggested readings to supplement this book; second, 

literature used in preparing this book, arranged by 

chapters.

Offices for information

State Geological Surveys (or equivalents) and District Offices 

of the U.S. Geological Survey Water Resources Division

State State Organization

Alabama Geological Survey of Alabama 

P.O. Drawer O 

University, AL 35486 

(205) 349-2852

Alaska Division of Geological and

Geophysical Surveys 

3001 Porcupine Drive 

Anchorage, AK 99501 

(907) 274-8602

Arizona Arizona Bureau of Geology 

and Mineral Technology 

University of Arizona 

Tucson, AZ 85721 

(602) 884-1401

Arkansas Arkansas Geological Commission Rm. 2301 Federal Office Bldg.

California

Colorado

Connecticut

Delaware

Florida

Georgia

Hawaii

Idaho

Illinois

Indiana

District Office

1317 McFarland Blvd. East 

Tuscaloosa, AL 35401 

(205) 759-5739

218 E Street 

Anchorage, AK 99501 

(907) 277-5526

Federal Bldg. 

301 W. Congress St. 

Tucson, AZ 85701 

(602) 792-6671

Vardelle Parham Geological

Center

3815 W. Roosevelt Road 

Little Rock, AR 72204 

(501) 371-1488

California Department of 

Conservation

700 W. Capital Ave. 

Little Rock, AR 72201 

(501) 378-5246

855 Oak Grove Ave.

Menlo Park, CA 94025 

Division of Mines and Geology (415) 323-8111, ext. 2326 

Resources Buildings, Room 1341 

1416 Ninth Street 

Sacramento, CA 95814 

(916) 445-1825

Colorado Geological Survey Bldg. 53 Denver Federal Center 

1313 Sherman Street, Room 715 Box 25046, STOP 415

Iowa

Denver, CO 80203 

(303) 892-2611

Department of Environmental

Protection

State Office Building, Rm. 561 

Hartford, CT 06115 

(203) 566-3540

Delaware Geological Survey 

University of Delaware 

101 Penny Hall 

Newark, DE 19711 

(302) 738-2833

Department of Natural

Resources

903 W. Tennessee St. 

Tallahassee, FL 32304 

(904) 488-4191

Georgia Department of

Natural Resources 

Earth and Water Division 

19 Hunter St., S.W. 

Atlanta, GA 30334 

(404) 656-3214

Department of Land and

Natural Resources 

Division of Water and Land

Development 

P.O. Box 373 

Honolulu, HI 96809 

(808) 548-7533

Idaho Bureau of Mines and

Geology

Moscow, ID 83843 

(208) 885-6785 or 885-6195

Illinois State Geological Survey 

121 Natural Resources Building 

Urbana,IL 61801 

(217) 344-1481

Department of Natural

Resources 

Geological Survey 

611 N. Walnut Grove 

Bloomington, IN 47401 

(812) 337-2862

Iowa Geological Survey 

Geological Survey Building 

123 North Capitol 

Iowa City, IA 52242 

(319) 338-1173

Denver, CO 80225 

(303) 234-5092

Rm. 235 Post Office Bldg. 

135 High St. 

Hartford, CT 06103 

(203) 244-2528

Rm. 208 Carroll Bldg. 

8600 La Salle Rd. 

Towson, MD 21204 

(301) 828-1535

Suite F-240, 325 John Knox Rd. 

Tallahassee, FL 32303 

(904) 386-1118

6481 Peachtree Industrial Blvd. 

Doraville, GA 30360 

(404) 221-4858

5th Floor, 1833 Kalakaua Ave. 

Honolulu, HI 96815 

(808) 955-0251

Rm. 365 Federal Bldg. 

550 W. Fort St. 

Box 036

Boise, ID 83724 

(208) 384-1750

605 N. Neil St. 

P.O. Box 1026 

Champaign, IL 61820 

(217) 359-3918

1819 N. Meridian St. 

Indianapolis, IN 46202 

(317) 269-7101

Rm. 269 Federal Bldg. 

400 S. Clinton St. 

P.O. Box 1230 

Iowa City, IA 52240 

(319) 338-0581, ext. 521

State State Organization

Kansas Kansas Geological Survey 

Raymond C. Moore Hall 

1930 Ave. A, Campus West 

University of Kansas 

Lawrence, KS 66044 

(913) 864-3965

Kentucky Kentucky Geological Survey 

University of Kentucky 

307 Mineral Industries Bldg. 

120 Graham Avenue 

Lexington, KY 40506 

(606) 258-8991

Louisiana Louisiana Geological Survey 

Box G, University Station 

Baton Rouge, LA 70803 

(504) 389-5812

Maine Maine Geological Survey

State Office Bldg., Room 211 

Augusta, ME 04330 

(207) 289-2801

Maryland Maryland Geological Survey 

Merryman Hall,

Johns Hopkins University 

Baltimore, MD 21218 

(301) 235-0771

Massachusetts Department of Environmental

Quality Engineering 

Division of Waterways 

100 Nashua St., Room 532 

Boston, MA 02114

Michigan Michigan Department of

Natural Resources 

Geological Survey Division 

Stevens T. Mason Bldg. 

Lansing, Ml 48926 

(517) 373-1256

Minnesota Minnesota Geological Survey 

University of Minnesota 

1633 Eustis St. 

St. Paul, MN 55108 

(612) 373-3372

Mississippi Mississippi Geological Survey 

2525 No. West St. 

Drawer 4915 

Jackson, MS 39216 

(601) 354-6228

Missouri Missouri Geological Survey 

Division of Geology and

Land Surveys 

P.O. Box 250 

Rolla, MO 65401 

(314) 364-1752

Montana Montana Bureau of Mines

and Geology 

Montana College of Mineral

Science and Technology 

Butte, MT 59701 

(406) 792-8321

Nebraska Conservation and Survey

Division

University of Nebraska 

Lincoln, NE 68508 

(402) 472-3471

Nevada Nevada Bureau of Mines

and Geology 

University of Nevada 

Reno, NV 89507 

(702) 784-6691

New Department of Resources and 

Hampshire Economic Development

James Hall, University of 

New Hampshire

Durham, NH 03824

(603) 862-1216

New Jersey New Jersey Bureau of

Geology and Topography 

P.O. Box 2809 

Trenton, NJ 08625 

(609) 292-2576

District Office

1950 Ave. A-Campus West 

University of Kansas 

Lawrence, KS 66045 

(913) 864-4321

Rm. 572 Federal Bldg. 

600 Federal Pi. 

Louisville, KY 40202 

(502) 582-5241

6554 Florida Blvd. 

P.O. Box 66492 

Baton Rouge, LA 708% 

(504) 387-0181, ext. 281

Suite 1001, 150 Causeway St. 

Boston, MA 02114 

(617) 223-2822

208 Carroll Bldg. 

8600 La Salle Rd. 

Towson, MD 21204 

(301) 828-1535

Suite 1001, 150 Causeway St. 

Boston, MA 02114 

(617) 223-2822

2400 Science Parkway 

Red Cedar Research Park 

Okemos, Ml 48864 

(517) 372-1910, ext. 561

Rm. 1033 Post Office Bldg. 

St. Paul, MN 55101 

(612) 725-7841

430 Bounds St. 

Jackson, MS 39206 

(601) 969-4600

1400 Independence Rd. 

Rolla, MO 65401 

(314) 364-3680, ext. 185

Rm. 421 Federal Bldg. 

P.O. Box 1696 

Helena, MT 59601 

(406) 449-5263

Rm. 406 Federal Bldg. and

U.S. Courthouse 

100 Centennial Mall North 

Lincoln, NE 68508 

(402) 471-5082

227 Federal Bldg. 

705 N. Plaza St. 

Carson City, NV 89701 

(702) 882-1388

Suite 1001, 150 Causeway St. 

Boston, MA 02114 

(617) 223-2822

Rm. 420 Federal Bldg. 

402 E. State St. 

P.O. Box 1238 

Trenton, NJ 08607 

(609) 989-2162

91
State State Organization

New Mexico New Mexico State Bureau of

Mines and Mineral Resources 

New Mexico Tech 

Socorro, NM 87801 

(505) 835-5420

New York New York State Geological

Survey 

New York State Education

Bldg., Rm. 973 

Albany, NY 12224 

(518) 474-5816

North Carolina Department of Natural and

Economic Resources 

Office of Earth Resources 

P.O. Box 27687 

Raleigh, NC 27611 

(919) 829-3833

North Dakota North Dakota Geological

Survey

University Station 

Grand Forks, ND 58201 

(701) 777-2231

Ohio

Oklahoma

Oregon

Pennsylvania

Puerto Rico

Rhode Island

South Carolina

District Office

Rm. 815, Western Bank Bldg. 

505 Marquette NW 

P.O. Box 26659 

Albuquerque, NM 87125 

(505) 766-2246

Rm. 343 U.S. Post Office and

Courthouse Bldg. 

P.O. Box 1350 

Albany, NY 12201 

(518) 472-3107

Rm. 436 Century Station P.O. Bldg. 

P.O. Box 2857 

Raleigh, NC 27602 

(919) 755-4510

Rm. 332 New Federal Bldg. 

3d. St. and Rosser Ave. 

P.O. Box 778 

Bismarck, ND 58501 

(701) 255-4011, ext. 227

975 W. Third Ave. 

Columbus, OH 43212 

(614) 469-5553

State

South Dakota

Tennessee

Texas

Utah

Ohio Department of Natural

Resources

Division of Geological Survey 

Fountain Square, Bldg. 6 

Columbus, OH 43224 

(614) 469-5344

Oklahoma Geological Survey 

University of Oklahoma 

830 Van Vleet Oval, Rm. 163 

Norman, OK 73069 

(405) 325-3031

State Department of Geology

and Mineral Industries 

1069 State Office Bldg. 

Portland, OR 97201 

(503) 229-5580

Department of Environmental

Resources 

Bureau of Topographic and

Geologic Survey 

P.O. Box 2357 

Harrisburg, PA 17120 

(717) 787-2169

Servicio Geologico de Bldg. 652

Puerto Rico P.O. Box 34168 

Dept. de Recursos Naturales Ft. Buchanan, PR 00934 

Apartado 5887, Puerta de Tierra (809) 783-4660 

San Juan, PR 00906 

(809) 722-3142

Rm. 621, 201 NW 3d St. 

Oklahoma City, OK 73102 

(405) 231-4256

830 NE. Holladay St. 

P.O. Box 3202 

Portland, OR 97208 

(503) 234-3361, ext. 4776

4th Floor, Federal Bldg. 

228 Walnut St. 

P.O. Box 1107 

Harrisburg, PA 17108 

(717) 782-3468

Vermont

Virginia

Washington

West Virginia

Wisconsin

Wyoming

Graduate School of

Oceanography 

University of Rhode Island 

Kingston, Rl 02881 

(401) 722-3142

South Carolina Geological

Survey

Harbison Forest Road 

Columbia, SC 29210 

(803) 758-3257

Suite 1001,150 Causeway St. 

Boston, MA 02114 

(617) 223-2822

Suite 200, 2001 Assembly St. 

Columbia, SC 29201 

(803) 765-5966

District of 

Columbia

State Organization

South Dakota State

Geological Survey 

Science Center, University

of South Dakota 

Vermillion, SD 57069 

(605) 624-4471

Department of Conservation 

Division of Geology 

G-5 State Office Bldg. 

Nashville, TN 37219 

(615) 741-2726

Bureau of Economic Geology 

University of Texas at Austin 

University Station, Box X 

Austin, TX 78712 

(512) 471-1534

Utah Geological & Mineral

Survey 

State of Utah - Department

of Natural Resources 

606 Black Hawk Way 

Salt Lake City, UT 84108

(801) 581-6831

Office of State Geologist 

Agency of Environmental

Conservation 

Montpelier, VT 05602

(802) 828-3357

Division of Mineral Resources 

Natural Resources Building 

P.O. Box 3667 

Charlottesville, VA 22903 

(804) 293-5121

Department of Natural

Resources 

Geology and Earth Resources

Division

Olympia, WA 98504 

(206) 753-6183

West Virginia Geological 

and Economic Survey 

P.O. Box 879 

Morgantown, WV 26505 

(304) 292-6331

Wisconsin Geological and

Natural History Survey 

University of Wisconsin 

1815 University Ave. 

Madison, Wl 53706 

(608) 262-1705

Geological Survey of Wyoming 

P.O. Box 3008, University

Station

University of Wyoming 

Laramie, WY 82071 

(307) 742-2054

District Office

Rm. 231 Federal Bldg. 

P.O. Box 1412 

Huron, SD 57350 

(605) 352-8651, ext. 258

Rm. A-413 Federal Bldg. 

U.S. Courthouse 

Nashville, TN 37203 

(615) 749-5424

Rm. 649 Federal Bldg. 

300 E. 8th St. 

Austin, TX 78701 

(512) 397-5766

Rm. 8002 Federal Bldg. 

125 S. State St. 

Salt Lake City, UT 84138 

(801) 524-5663

Suite 1001,150 Causeway St. 

Boston, MA 02114 

(617) 223-2822

Rm. 304, 200 W. Grace St. 

Richmond, VA 23220 

(804) 782-2427

Suite 600, 1201 Pacific Ave. 

Tacoma, WA 98402 

(206) 593-6510

Rm. 3017 Federal Bldg. and

U.S. Courthouse 

500 Quarrier St. East 

Charleston, WV 25301 

(304) 343-6181, ext. 310

Rm. 200, 1815 University Ave. 

Madison, Wl 53706 

(608) 262-2488

4020 House Ave. 

P.O. Box 2087 

Cheyenne, WY 82001 

(307) 778-2220, ext. 2111

208 Carroll Bldg. 

8600 La Salle Rd. 

Towson, MD 21204 

(301) 828-1535

Public Inquiries Offices of the U.S. Geological Survey

Anchorage, Alaska Rm. 108 Skyline Bldg. 

502 2d Avenue 

Anchorage, AK 99501

(907) 277-0577 Washington, District of Rm. 1028 GSA Bldg. 

Columbia 19th & F Sts. NW

Washington, DC 20244

(202) 343-8073

Los Angeles, California Rm. 7638 Federal Bldg. (213) 688-2850 

300 No. Los Angeles St. 

LosAngeles,CA90012

Menlo Park, California Bldg. 3, MS 33

345 Middlefield Rd. 

Menlo Park, CA 94025

(415)323-8111

San Francisco, 

California

Rm. 504 Custom House (415) 556-5627

555 Battery Street

San Francisco, CA 94111

Dallas, Texas

Salt Lake City, Utah

Reston, Virginia

Rm. 1C45 Federal Bldg. (214) 749-3230 

1100 Commerce St. 

Dallas, TX 75202

Rm. 8105 Federal Bldg.

125 S. State St.

Salt Lake City, UT 84128

Rm. 1C402 National 

Center STOP 302 

12201 Sunrise Valley Dr. 

Reston, VA 22092

(801) 524-5652

(703) 860-6167

Denver, Colorado Rm. 1012 Federal Bldg. (303)837-4169 

1961 Stout Street 

Denver, CO 80294

Spokane, Washington Rm. 678 U.C. Courthouse (509) 456-2524 

W. 920 Riverside Avenue 

Spokane, WA 99201

92
References

Suggested reading

Genera/

Assessment of Research on Natural Hazards, by 

Gilbert F. White and J. Eugene Haas, Cambridge, 

Mass., Massachusetts Institute of Technology

Press, 1975, 470 p. For the general reader.

Design with Nature, by lan McHarg, Garden City, 

New York, Doubleday/Natural History Press, 

1969, 197 p. Pioneer work on recognition of natural factors 

in land planning.

Environmental Geology Conservation, Land-Use 

Planning, and Resource Management, by Peter T. 

Flawn, New York, Harper and Row, 1970, 311 p. 

College-level text.

Cities and Geology, by Robert F. Legget, New York, 

McGraw Hill, 1973, 552 p. College-level text in engineering geology.

Environmental Geology, by Edward A. Keller, Columbus, Ohio, Merrill Publishing Co., 1976,488 p. 

Co//ege-/eve/ text.

Geology, Resources, and Society, by H. W. Menard, 

San Francisco, W. H. Freeman and Co., 1974, 

621 p. College-level text for nonmajors in earth science.

Earth-Science Information in Land-Use Planning, 

Guidelines for Earth Scientists and Planners, by 

William Spangle and others, U.S. Geological 

Survey Circular 721, 1976, 28 p. Free on application 

to Branch of Distribution, U.S. Geological Survey, 1200 S. fads 

St., Arlington, VA 22202.

Environmental Planning and Geology, D. R. Nichols 

and C. C. Campbell, eds., Washington, D.C. U.S. 

Government Printing Office, 1971, 204 p. A collection of articles on engineering geology as related to urban 

planning.

United States Geological Survey Offers Services For 

Planners, by William J. Kockelman, in "Practicing 

Planner," December 1976, p. 10-15.

On specific areas, but with wide application

Environmental Geology and Hydrology, Huntsville 

and Madison County, Alabama, Geological Survey of Alabama, Atlas Series 8, University, Alabama, 1975, 118 p.

Geology and Ground Water for Land-Use Planning in 

the Eagle River-Chugiak Area, Alaska, by Chester 

Zenone and others, U.S. Geological Survey, 

Greater Anchorage Area Borough, Alaska, 1974, 

25 p.

Use of Natural Resource Data in Land and Water 

Planning, by D. E. Hill and H. E. Thomas, Bulletin 

733 of the Connecticut Agricultural Experiment 

Station, 1972.

Geology for Planning in McHenry County, Illinois, by 

J. E. Hackett and M. R. McComas, Illinois Geological Survey Circular 438, Urbana, Illinois, 1969, 

31 p.

Medford Performance Requirements for the Maintenance of Social Values Represented by the 

Natural Environment of Medford Township, New 

Jersey, by Narendra Juneja, Medford Township 

Office, Medford, N.J., 1974.

Environmental Geology for Land-Use Planning, by 

A. R. Geyer and W. G. McGlade, Environmental 

Geology Rept. 2 of the Pennsylvania Dept. of 

Environmental Resources, Harrisburg, 1972,44 p.

Use of USGS Earth-Science Products by County Planning Agencies in the San Francisco Bay Region, 

California, by W. J. Kockelman, U.S. Geological 

Survey Open-File Report No. 76-547,1976,185 p.

Guidelines and Criteria for Identification and LandUse Controls of Geologic Hazard and Mineral 

Resource Areas, by W. P. Rogers and others, 

Special Publication No. 6, Colorado Geological Survey, 1974, 146 p.

Approaches to Environmental Geology, E. G. Wermund, editor, Report of Investigations No. 81, 

University of Texas, Austin, 1974, 268 p.

On specific topics

Maps and Man, by N. J. W. Thrower, Prentice-Hall,

1972. for the general reader. 

Mapping, by David Greenhood, University of

Chicago Press, 1964. For the general reader. 

A Primer on Water, by L. B. Leopold, W. H. Freeman,

1974, 172 p. for the general reader.

Flood-Prone Areas and Land-Use Planning Selected 

Examples from the San Francisco Bay Region, 

California, by A. O. Waananen and others, 1977, 

U.S. Geological Survey Prof. Paper 942, 75 p. 

Professional level.

Selection of Refuse Disposal Sites in Northeastern 

Illinois, by G. M. Hughes, Illinois State Geological 

Survey Environmental Geology Notes No. 17,

1967, 26 p. Includessummary of landfill studies from many 

places. Professional level.

From Town Dump to Sanitary Landfill: A Case History, 

by R. M. Foose, Bulletin of the Association of 

Engineering Geologists, vol. 9, no. 1,1972, p. 1-16. 

Professional level.

Introduction to Tunnel Geology Rock Defects and 

Loads on Tunnel Supports, by Karl Terzaghi, in 

Rock Tunneling with Steel Supports, by R. V. 

Proctor and T. L. White, Youngstown, Ohio, 

Commercial Shearing and Stamping Co., 1946,

p. 17-99. Professional level.

Mapping Geological Conditions in Tunnels, by Richard 

J. Proctor, Bulletin of the Association of Engineering Geologists, V. 8, no. 1, p. 1-43. Professional level.

Literature used in preparing this book, arranged by chapters

Introduction

The tabulated estimates of losses from geologic 

hazards are from a variety of sources. Those for 

floods, earthquakes, volcanoes, and "others" are 

from Assessment of Research on Natural Hazards, by 

White and Haas, 1975 (cited in "Suggested Reading"). 

The estimate for landslide damage is from a 

manuscript by Robert Schuster, Chief, Branch of 

Engineering Geology, U.S. Geological Survey. The 

estimate is conservative; for example, landslide 

damage in the winter of 1968-69 in the San Francisco 

Bay region alone totalled at least $25,400,000 (F. A. 

Taylor and E. E. Brabb, 1972, Map Showing Distribution and Cost by Counties of Structurally Damaging 

Landslides in the San Francisco Bay Region, California, Winter of 1968-69: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-327).

The estimate for damage due to expansive soils is 

from Expansive Soils and Housing Development, by 

D. E. Jones, Jr., 1973, in Proceedings of Workshop on 

Expansive Clays and Shales in Highway Design and 

Construction, v. 1. The estimates for landslides and 

expansive soils probably overlap somewhat, owing to 

differences in definitions.

The estimate of losses of mineral resources in 

California due to urbanization is from Urban Geology 

Master Plan for California: The Nature, Magnitude, 

and Costs of Geologic Hazards in California and 

Recommendations for their Mitigation, by J. T. Alfors, 

J. L. Burnett, andT. E. Gay, Jr., 1973, Bulletin 198 of the 

California Division of Mines and Geology.

Damaging earthquakes map: Earthquake History of 

the United States, Pub. 41-1, National Oceanic and 

Atmospheric Administration, Environmental Data 

Service, Revised 1970 Edition, 1973.

Landslide and landslide potential map: Prepared by 

Dorothy Radbruch-Hall, based on Preliminary Landslide Overview Map of the Conterminous United 

States, by D. H. Radbruch-Hall and others, 1976, U.S. 

Geological Survey, MF-771.

Swelling clay map: modified from Geologic Origin 

and Distribution of Swelling Clays, by H. A. Tourtelot, 

1974, Association of Engineering Geologists Bulletin, 

v. 11, no. 4.

The material on "Reading And Obtaining Topographic Maps" has been taken, with minor modifications, from the U.S. Geological Survey leaflet, 

Topographic Maps.

The discussion on "Orientation, Scale, Detail, And 

Accuracy of Maps" owes much to Earth Science 

Information in Land-Use Planning, by William 

Spangle and Associates; F. Beach Leighton and 

Associates; and Baxter, McDonald and Company, 

1976, U.S. Geological Survey Circular 721.

The discussion of "Land-Use And Land-Cover 

Maps" has been largely paraphrased from a Land-Use 

and Land Cover Classification System for Use with 

Remote Sensor Data, by James R. Anderson, Ernest E. 

Hardy, John T. Roach, and Richard E. Witmer, 1976, 

U.S. Geological Survey Professional Paper 964.

The material on "Flood-Prone Area Maps" has 

been abstracted from Index and Description of 

Flood-Prone Area Maps in theTucson, Phoenix Area, 

Arizona, by E. S. Davidson, 1973, U.S. Geological 

Survey Map 1-843-A.

The geologic map of part of the Monterey 

quadrangle is slightly modified from Preliminary 

Geologic Map of the Monterey and Seaside 7.5- 

Minute Quadrangles, Monterey County, California, 

with Emphasis on Active Faults, by J. C. Clark, T. W. 

Dibblee, Jr., H. G. Green, and O. E. Bowen, Jr., 1974,

U.S. Geological Survey Miscellaneous Field Studies 

Map MF-577. The cross-section accompanying the 

geologic map was drawn by T. W. Dibblee, Jr., and the 

block diagram of the same area is based on an 

isometric projection by Tau Rho Alpha.

Central San Mateo County, California

Alfors, J. T., Burnett, J. L., and Gay, T. E., Jr., 1973,

Urban geology master plan for California: Calif.

Div. Mines and Geology Bull. 198, 112 p. 

Borcherdt, R. D., ed., Studies for seismic zonation of

the San Francisco Bay region: U.S. Geol. Survey

Prof. Paper 941-A, 102 p. 

Brabb, E. E., and Pampeyan, E. H., 1972a, Preliminary

geologic map of San Mateo County, California:

U.S. Geol. Survey Misc. Field Studies Map

MF-328, scale 1:62,500. 

 1972b, Preliminary map of landslide deposits

in San Mateo County, California: U.S. Geol.

Survey Misc. Field Studies Map MF-344, scale

1:62,500. 

Brabb, E. E., Pampeyan, E. H., and Bonilla, M. G., 1972,

Landslide susceptibility in San Mateo County,

California: U.S. Geol. Survey Misc. Field Studies

Map MF-360, scale 1:62,500. 

California Coastal Zone Conservation Commissions,

1975, California Coastal Plan: State of California,

443 p. 

California Division of Mines and Geology, 1974 and

1975, Special Studies Zones maps, San Francisco

South, Montara Mountain, San Mateo, Half

Moon Bay, Woodside,and Palo Alto quadrangles,

scale 1:24,000. 

California Legislature Joint Committee on Seismic

Safety, 1974, Meeting the earthquake challenge:

State of California, 223 p.

93
Cluff, L. S., and Bolt, B. A., 1969, Risk from earthquakes 

in the modern urban environment, with special 

emphasis on the San Francisco Bay area, in 

Danehy, E. A., ed., Urban Environmental Geology 

in the San Francisco Bay Area: Assoc. Eng. Geolor 

gists, Spec. Publ., p. 25-64.

Hart, E. W., 1975, Fault hazard zones in California: 

Calif. Div. Mines and Geology, Spec. Pub. 42, 

Revised Edition, 42 p.

Hershman, M. J., 1975, Coastal zone management 

accommodating competing coastal uses: Geoscience and Man, v. 12, p. 109-115.

lacopi, Robert, 1964, Earthquake Country: Lane Book 

Co., Menlo Park, Calif., 192 p.

Ketcham, B. H., ed., 1972, The water's edge critical 

problems of the coastal zone: Cambridge, Mass., 

MIT Press, 393 p.

Lawson, A. C., and others, 1908, The California earthquake of April 18, 1906: Report of the State 

Earthquake Investigation Commission, v. 1, 

p. 92-104.

Los Angeles Planning Commission, 1975, Preliminary 

ordinance draft to regulate density according to 

the percentage of slope: Los Angeles City Plan 

Case No. 25652, 12 p.

Nichols, D. R., and Buchanan-Banks, J. M., 1974, Seismic hazards and land-use planning: U.S. Geol. 

Survey Circ. 690, 33 p.

Nichols, D. R., and Edmundson, J. R., 1975, Text to 

slope map of part of west-central King County, 

Washington: U.S. Geol. Survey Misc. Geol. Inv. 

Map 1-852-E, scale 1:48,000.

Nilsen, T. H., and Turner, Barbara, 1976, Influence of 

rainfall and ancient landslide deposits on recent 

landslides (1950-1971) in urban areas of Contra 

Costa County: U.S. Geol. Survey Bull. 1388,18 p.

President's Council on Environmental Quality, 1975, 

Environmental Quality: Sixth Annual Report, 

763 p.

San Mateo City-County Task Force, 1975, Seismic and 

safety elements of the general plan (draft): San 

Mateo County, 2 volumes.

Spangle, William, and Associates; Leighton, F. B., and 

Associates; and Baxter, McDonald, and Company, 

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

U.S. Geol. Survey Circ. 721, 28 p.

Steinbrugge, K. V., 1968, Earthquake hazard in the 

San Francisco Bay area: Univ. Calif. Berkeley, 

Inst. of Govt. Studies, 80 p.

Taylor, F. A., and Brabb, E. E., 1972, Maps showing 

distribution and cost by counties of structurally 

damaging landslides in the San Francisco Bay 

region, California, winter of 1968-1969: U.S. 

Geol. Survey Misc. Field Studies Map MF-327, 

scales 1:1,000,000 and 1:500,000.

Tinsley, J. C., 1972, Sea cliff erosion as a measure of 

coastal degradation, San Mateo County, California: Stanford Univ., unpub. student research 

report, 88 p.

U.S. Coast and Geodetic Survey, 1969, Studies in 

seismicity and earthquake damage statistics, 

1969 Summary and recommendations, 23 p.

Woolfe, D. A., 1973, Adoption of the resource conservation area density matrix and statement of 

policy: San Mateo County interdepartmental 

memo, 18 p.

Tucson, Arizona

Anderson, T. W., 1972, Electrical-analog analysis of 

the hydrologic system, Tucson Basin, southeastern Arizona Water resources of the Tucson 

Basin: U.S. Geol. Survey Water Supply Paper 

1939-A, 34 p.

Arizona Bureau of Mines, 1976, Preliminary map 

showing potential for copper deposits in the 

Tucson 2° quadrangle: U.S. Geol. Survey openfile map, 76-458, scale 1:250,000.

Brown, S. G., 1976, Components of the water budget 

in the Tucson area, Arizona, 1970-72: U.S. Geol. 

Survey Misc. Geol. Inv. Map I-844M, scale 

1:250,000.

Burkham, D. E., 1970, Depletion of streamflow by 

infiltration in the main channels of the Tucson 

Basin: U.S. Geol. Survey Water Supply Paper 

1939-B, 36 p.

Condes de la Torre, Alberto, 1970, Streamflow in the 

upper Santa Cruz River basin, Santa Cruz and 

Pima Counties, Arizona Water resources in the 

Tucson Basin: U.S. Geol. Survey Water Supply 

Paper 1939-A, 26 p.

Davidson, E. S., 1973a, Geohydrology and water resources of the Tucson Basin,-Arizona Water 

resources of the Tucson Basin: U.S. Geol. Survey 

Water Supply Paper 1939-E, 81 p.

 1973b, Index and description of flood-prone 

area maps in the Tucson-Phoenix area, Arizona: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-843-A, 

scale 1:500,000 with examples at larger scales.

Johnson, R. C., 1976, Users guide to the hillside development zone for Pima County, Arizona: Pima 

County Planning Dept. Prepared for the Board of 

Supervisors, Pima County, Arizona, 23 p.

Laney, R. L., 1972, Chemical quality of the water in the 

Tucson Basin, Arizona Water resources of the 

Tucson Basin: U.S. Geol. Survey Water Supply 

Paper 1939-D, 46 p.

National Academy of Science National Academy of 

Engineering, Committee on Water Quality 

Criteria: 1973, Water quality criteria 1972: Washington, D.C. Environmental Protection Agency, 

594 p.

Osterkamp, W. R., 1973a, Map showing depth to 

water in wells in the Tucson area, Arizona, 1972: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-844-D, 

scale 1:250,000.

 1973b, Map showing distribution of recoverable 

ground water in the Tucson area, Arizona: U.S. 

Geol. Survey Misc. Geol. Inv. Map 1-844-F, scale 

1:250,000.

Osterkamp, W. R., and Laney, R. L., 1974, Map showing chemical quality of ground water for public 

supply in the Tucson area, Arizona: U.S. Geol. 

Survey Misc. Geol. Inv. Map 1-844-L, scale 

1:250,000.

U.S. Environmental Protection Agency, 1975, National 

interim primary drinking water regulations: 

Federal Register, v. 40, no. 248, p. 59566-59574.

U.S. Geological Survey, 1973, Slope map of Cat 

Mountain quadrangle, Arizona: Prepared for 

Arizona Resources Information Systems, Phoenix, 

Arizona, scale 1:24,000.

U.S. Geological Survey, 1973, Map showing potential 

for copper deposits in the eastern three-quarters 

of the Nogales 2° quadrangle, Tucson area, 

Arizona: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-844-G, scale 1:250,000.

Front Range Urban Corridor, 

Colorado

Colton, R. B., and Fitch, H. R., 1974, Map showing 

potential sources of gravel and crushed-rock 

aggregate in the Boulder-Fort Collins-Greeley 

area, Front Range Urban Corridor, Colorado: 

U.S. Geol. Survey Misc. Inv. Map 1-855-D, scale 

1:100,000.

Colton, R. B., and Lowrie, R. L., 1973, Map showing 

mined areas of the Boulder-Weld coal field, 

Colorado: U.S. Geol. Survey Misc. Field Studies 

Map MF-513, scale 1:24,000.

Hart, S. S., 1974, Potentially swelling soil and rock in 

the Front Range Urban Corridor, Colorado: 

Colorado Geol. Survey Environmental Geology 

Rept. 7, 23 p.

Jones, D. E., Jr., and Holtz, W. G., 1973, Expansive soils 

 the hidden disaster: Civil Engineering, v. 43, 

no. 8, p. 49-51.

Livingston, R. K., Klein, J. M., Bingham, D. L., 1976, 

Water resources of El Paso County, Colorado: 

Denver, Colorado, Colorado Water Resources 

Circular 32, 85 p.

Lowrie, R. L., 1966, Analysis of the coal industry in 

Boulder-Weld Coalfield, Colorado: U.S. Bur. 

Mines Rept. Inv. 6726, 79 p.

Malde, H. E., 1955, Surficial geology of the Louisville 

quadrangle, Colorado: U.S. Geol. Survey Bull. 

996-E, p. 217-259.

Schwochow, S. D., Shroba, R. R., and Wicklein, P. C., 

1974, Atlas of sand, gravel, and quarry aggregate 

resources, Colorado Front Range counties: 

Colorado Geol. Survey Spec. Pub. 5-B, unpaged.

Trimble, D. E., and Fitch, H. R., 1974, Map showing 

potential sources of gravel and crushed-rock 

aggregate in the Greater Denver Area, Front 

Range Urban Corridor, Colorado: U.S. Geol. 

Survey Misc. Inv. Map 1-856-A, scale 1:100,000.

Connecticut River valley

Colton, R. B., 1960, Surficial geology of the Windsor 

Locks quadrangle, Connecticut: U.S. Geol. Survey Geol. Quad. Map GQ-137, scale 1:24,000.

Cushman, R. V., 1964, Ground-water resources of 

north-central Connecticut: U.S. Geol. Survey 

Water-Supply Paper 1752, 96 p. and plates.

Federal Inter-Agency River Basin Committee, 1951, 

Inter-agency coordination of drainage area data: 

Notes on Hydrologic Activities, Bull. No. 4, 48 p.

Hill, D. E., and Thomas, H. F., 1972, Use of natural 

resources data in land and water planning: 

Connecticut Agricultural Experiment Station 

Bull. no. 733, 47 p.

Johnson, L. H., Cook, D. T., and Walther, Lincoln, 

1976, Plan of development, Town of East Granby, 

Connecticut: Conn. Dept. of Community Affairs 

rept. no. DCA 76-28.

O'Leary, D. W., 1973, Map showing unconsolidated 

materials, Deep River Quadrangle, Connecticut: 

U.S. Geol. Survey Misc. Field Studies Map MF524, scale 1:24,000.

Pessl, Fred, Jr., Langer, W. H., and Ryder, R. B., 1971, 

Geologic and hydrologic maps for land use planning in the Connecticut Valley with examples 

from the folio of the Hartford North quadrangle, 

Connecticut: U.S. Geol. Survey Circular 674, 

12 p.

Randall, A. D., 1964, Geology and ground water in 

The Farmington-Granby area, Connecticut: 

U.S. Geol. Survey Water-Supply Paper 1661, 

130 p. and plates.

 1970, Surficial geologic map of the Tariffville 

quadrangle, Connecticut-Massachusetts: U.S. 

Geol. Survey Geol. Quad. Map GQ-798, scale 

1:24,000.

Shearin, A. E., and Hill, D. H., 1962, Soil survey of 

Hartford County, Connecticut: U.S. Soil Conservation Service, ser. 1958, 14, 126 p., with map 

folio.

Thomas, M. P., 1966, Effect of glacial geology upon 

the time distribution of streamflow in eastern and 

southern Connecticut: U.S. Geol. Survey Prof. 

Paper 550-B, p. B209-212.

Thomas, M. P., and Palmer, J. E., 1974, Map showing 

drainage areas Deep River quadrangle, Connecticut: U.S. Geol. Survey Misc. Field Studies Map 

MF-524-C, scale 1:24,000.

Nassau County, Long Island, 

New York

Cohen, Philip, and Durfor, C. N., 1966, Design and 

construction of a unique injection well on Long 

Island, New York: U.S. Geol. Survey Prof. Paper 

550-D, p. 253-257.

Cohen, Philip, Franke, O.L., and Foxworthy, B. L., 

1968, An atlas of Long Island's water resources: 

New York Water Resources Comm. Bull. 62, 

117 p.

 1970, Water for the future of Long Island, New 

York: New York Water Resources Comm. Bull. 

62A, 36 p.

Cohen, Philip, Franke, O.L., and McClymonds, N. E., 

1969, Hydrologic effects of the 1962-66 drought 

on Long Island, New York: U.S. Geol. Survey 

Water Supply Paper 1879-F, 18 p.

Franke, O. L., 1968, Double-mass-curve analysis of 

the effects of sewering on ground-water levels 

on Long Island, New York, in Geological Survey 

Research, 1968: U.S. Geol. Survey Prof. Paper 

600-B, p. B205-209.

Franke, O. L., and McClymonds, N. E., 1971, Summary 

of the hydrologic situation on Long Island, New 

York, as a guide to water-management alternatives: U.S. Geol. Survey Prof. Paper 627-F, 59 p.

Fuller, M. L., 1914, The geology of Long Island, New 

York: U.S. Geol. Survey Prof. Paper 82, 231 p.

94
Kimmel, G. E., 1971, Water-level surfaces in the aquifers of western Long Island, New York, in 1959 

and 1970, in Geological Survey Research, 1971: 

U.S. Geol. Survey Prof. Paper 750-B, p. B224-228.

Ku, H. F. H., Vecchioli, John, and Cerrillo, L A., 1975, 

Hydrogeology along the proposed barrierrecharge-well alignment in southern Nassau 

County, Long Island, New York: U.S. Geol. Survey, Hydrologic Inv. Atlas HA-502.

Lusczynski, N. J., 1966, Salt-water encroachment in 

southern Nassau and southeastern Queens 

Counties, Long Island, New York: U.S. Geol. 

Survey Water-Supply Paper 1613-F, 76 p.

McClymonds, N. E., and Franke, O. L., 1971, Watertransmitting properties of Long Island's aquifers: 

U.S. Geol. Survey Prof. Paper 627-E, 24 p.

Miller, J. F., and Frederick, R. H., 1969, The precipitation regime of Long Island, New York: U.S. Geol. 

Survey Prof. Paper 627-A, 21 p. -

Perlmutter, N. M., and Koch, Ellis, 1972, Preliminary 

hydrologic appraisal of nitrate in ground water of 

southern Nassau County, Long Island, New York, 

in Geological Survey Research, 1972: U.S. Geol. 

Survey Prof. Paper 800-B, p. B225-B235.

Perlmutter, N. M., and Lieber, Maxim, 1970, Dispersal 

of plating wastes and sewage contaminants in 

ground water and surface water, South Farmingdale-Massapequa area, Nassau County, New 

York: U.S. Geol. Survey Water-Supply Paper 

1879-G, 67 p.

Perlmutter, N. M., Pearson, F. J., and Bennett, G. D., 

1968, Deep-well injection of treated waste water

 an experiment in re-use of ground water in 

western Long Island, New York: New York Geol. 

Assoc. Guidebook, 40th Ann. Mtg., p. 221-231.

Seaburn, G. E., 1970, Preliminary results of hydrologic 

studies at two recharge basins on Long Island, 

New York: U.S. Geol. Survey Prof. Paper 627-C, 

17 p.

Vecchioli, John, 1972, Experimental injection of 

tertiary-treated sewage in a deep well at Bay 

Park, Long Island, New York a summary of early 

results: Jour. New England Water Works Assoc., 

v. 86, no. 2, p. 87-103.

Fairfax County, Virginia

Force, L. M., and Froelich, A. J., 1975, Preliminary 

surface materials map of the Annandale quadrangle, Virginia: U.S. Geol. Survey open-file 

map 75-255, scale 1:24,000.

Huffman, A. C., Froelich, A. J., and Force, L. M., 1975, 

Preliminary geologic map of the Annandale 

quadrangle, Virginia: U.S. Geol. Survey openfile map 75-254, scale 1:24,000.

Johnston, R. H., and Larson, J. D., 1976, Preliminary 

appraisal of ground water in the Franconia area, 

Virginia: U.S. Geol. Survey open-file report 

76-400, 19 p.

Obermeier, S. F., and Froelich, A. J., 1976, Preliminary 

geologic and engineering review of the Franconia area, Fairfax County, Virginia: U.S. Geol. 

Survey open-file report 76-273, lip.

Office of Comprehensive Planning, Fairfax County,

Virginia, 1974, Land-use map of Lower Potomac, 

Mount Vernon, Rose Hill, and Springfield planning districts: Dept. of Environmental Management, Fairfax, Virginia.

1975a, Area IV preliminary plan, land use and 

transportation proposal: Dept. of Environmental 

Management, Fairfax, Virginia, p. 21, 22, 44, 45 

and a composite map. 

-1975b, Revisions to the preliminary plan for

area IV as adopted by Board of Supervisors on 

July 28, 1975: Dept. of Environmental Management, Fairfax, Virginia, p. 42, 43 and map revisions.

Porter, H. C., Derting, J. F., Elder, J. H., Henry, E. F., 

and Pendleton, R. F., 1963, Soil survey of Fairfax 

County, Virginia: U.S. Soil Conserv. Service, 

Dept. of Agriculture, 103 p.

Rogers, H. G., 1975, Landforms map of the Annandale 

quadrangle, Virginia: U.S. Geol. Survey openfile map 75-157, scale 1:24,000.

U.S. Geological Survey, 1974, Map of flood-prone 

areas, Annandale quadrangle, Virginia: Available 

on request from U.S. Geol. Survey District office, 

Richmond. VA, scale 1:24,000.

 1975, Topographic maps: Washington, U.S. 

Govt. Printing Office, 20 p. 

-1976, Annandale quadrangle, Virginia, 7.5-

minute series, (topographic), scale 1:24,000, 

photorevised 1971.

Varnes, D. J., 1958, Landslide types and processes, in 

Eckel, E. B., ed., Landslides and engineering 

practice, ch. 3, p. 20-47, Washington, Highway 

Research Board Special Rept. 29, NAS-NRC 

544.

95
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I

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Spreading urbanization in

Looking north, from above Saratoga toward Sunnyvale. Airplane hangars at 

Moffett Field Naval Air Station at left background, with tidal flats at south end 

of San Francisco Bay beyond. When the photograph at left was taken in 7959, 

the area was mostly orchard, but urbanization had already begun, spreading 

from San )ose off to the right, and from Moffett Field. By 7977, when the photo-
-d ^ 'SVj' * ij,,

i - >f"«i

Santa Clara County, California

I

graph at r/ght was taken, nearly all the land except the tidal flats had been 

developed. Exchanging fruit trees for buildings and pavement changes much 

more than the scenery. When those changes are anticipated and the development is guided by knowledge of the controlling geologic and hydrologic 

conditions, it is certain to be more economical, safer, and cleaner. (Photographs 

courtesy Air Photo Co., Mountain View, Calif.)