GEOLOGICAL SURVEY CIRCULAR 487 

GROWING IMPORTANCE OF 

URBAN GEOLOGY 

GROWING IMPORTANCE OF URBAN GEOLOGY 

By John T. McGill 

GEOLOGICAL SURVEY CIRCULAR 487 

Washington 1964 
United States Department of the Interior 

STEWART l. UDALL, Secretory 

Geological Survey 

William T. Pecora, Director 

REPRINTED 

1964 

1966 

Free on applicotion fo the U.S. Geological Sunwy, Washington, D.C. 20242 
GROWING IMPORTANCE OF URBAN GEOLOGY 

By John T. McGill 

CONTENTS 

Page 

Urban growth and its implicat1ons . . . . . . . • 

The Los Angeles area-an outstanding example . . 2 

2 

3 

3 

4 

Man versus nature ..... . 

Urban engineering geology .. 

Lessons to be learned . . • . 

Meeting the national need for urban geologic information. 

Urban geology is much too broad a subject to 

cover comprehensively or in any satisfactory detail 

in a short presentation. It has been with us for many 

years» yet possesses a timeliness and an urgency that 

is regrettably little appreciated. The purpose of this 

brief paper, therefore, is to alert the geological profession, and others, to the present and future significance of what has been until recently a relatively minor 

field of applied geology. I hope to increase not only 

your awareness, but your concern, for concern is 

surely warranted. 

URBAN GROWTH AND ITS IMPLICATIONS 

Urban geology 1s growing in importance in the 

United States primarily because urban areas are growing. Urban areas are growing because the population 

of the nation is increasing and also because proportionally more people are congregating in urban areas. 

The critical factors are the phenomenal rate, magnitude, and changing pattern of urban population growth 

that have developed in recent decades. The trends 

are well documented in the census records. 

For more than a hundred years, the urban population has grown more rapidly than the rural, until 

today approximately 70 percent of our inhabitants live 

in urban areas. From 1950 to 1960» the total population of the United- States grew from nearly 151 million 

to over 179 million, an increase of well over 28 million, or 19 percent. In the same period, the urban 

population grew from nearly 96}2 million to over 125 

million, an increase of nearly 29 million, or 30 percent. All the nation's massive population increase 

during this 10-year interval occurred in urban areas. 

Adapted from a talk presented at the 75th Annual 

Meeting of the Geological Society of America. New 

York, N. Y., November 18, 1963. 

A notable feature of current urban growth is that 

it is predominantly metropolitan, and furthermore is 

concentrated in the very largest metropolitan area-s. 

Of the total papulation increase for the United States 

from 1950 to 1960, over 84 percent occurred in the 

212 Standard Metropolitan Statistical Areas, each of 

which contains at least one city of 50,000 inhabitants 

or more. But within these metropolitan areas the 

growth rate was very uneven. The population of the 

central cities increased by about 9 percent, while 

that of the suburban fringes grew by a spectacular 

48 percent. Expressed another way, and perhaps more 

meaningfully» roughly two-thirds of the entire population growth of the United States since 1950 has been 

taking place in the suburbs. There is no reason to 

expect any slowing down in the foreseeable future; 

indeed, acceleration is much more likely. 

If the data on population growth and trends seem 

surprising, the implications are almost overwhelming. 

The rapidity and the changing pattern of urban growth 

have given rise to unprecedented problems of city and 

regional planning in the course of suburban development and urban renewal andredevelopment. Theplanning problems are noteworthy for their magnitude, 

diversity, and complexity, but it will suffice here to 

mention only a few of the areas of greatest difficulty, 

by way of illustration. Transportation and traffic 

probably constitute the for em o s t problem in most 

growing cities. Also high on the list is the expansion 

of the various basic city services and utilities, especially water supply, sewerage and sewage disposal, 

and drainage, including flood control. An immediate 

concern in the suburbs is the acquisition of appropriate sites for s c h o o 1 s and other essential public 

facilities and for recreational purposes well in advance of local population growth. 

Clearly most problems of physical planning are, 

or soon become, problems of engineering. Therefore 
the physical planning process necessarily is based to 

a large degree on engineering principles and practices. 

Many city planners are, in fact, civil engineers. Since 

1923, early in the history of modern cityplanning, the 

American Society of Civil Engineers has sponsored a 

technical division on city planning. Planners, because 

of their overlap of interests, are coming to realize 

what civil engineers have been learning slowly and for 

a much longer time-the value of geologic information. 

A major phase of master planning is the evaluation of the advantages and disadvantages of one use of 

land as compared to another use, so as to make planning and zoning possible for the conservation and maximum beneficial use of land, our most fundamental natural resource. Sooner or later we all pay, directly or 

indirectly, for unintelligent use ofland. So we all have 

a stake in land-use planning. To a significant degree 

it is the characteristics of the earth materials underlying its surface that determine how land can be most 

effectively and safely used. Correlation of the requirements for potential use with pertinent geologic considerations will help assure that land use will not conflict with the limitations imposed by natural conditions. 

This is especially true when the easily developed sites 

are depleted and suburban expansion is forced into marginal or hilly areas, where new and more imposing 

difficulties are encountered. Factors other than geology commonly dictate a given use for land, but this 

may then make know ledge and consider at ion of the geology even more important. 

Problems of urban land use that are related to 

geology ultimately involye every aspect of civil engineering through their effect upon the_,design, construction, and maintenance of specific engineering works. 

Certain of these problems, such as earthquakes and 

some landslides, occur as natural geologic hazards 

inherent in the environment. Other problems, such 

as instability of cuts and ground-water pollution, pose 

actual or p'otential threats because of unwise or poorly 

planned activities of man. Still others may have more 

to do with the economics of land use or development 

than with its safety; problems of difficult excavation 

or lack of nearby sources of earth material suitable 

for fill are examples. 

The importance of geology to planning and to civil 

engineering obviously is very great, and is by no means 

limited to urban areas. On the other hand, it is essential to point out that not all applied urban geolo.gy is 

engineering geology. Sand and gravel and other raw 

materials of construction are a concern of engineering 

geologists. but the economic geology of any mineral 

resource occurring within an urban area may have a 

critical bearing on local land-use planning and development. Accessibility to valuable mineral lands or 

their preservation for future use often can be assured 

through judicious zoning and other regulations. 

THE LOS ANGELES AREA-AN 

OUTSTANDING EXAMPLE 

MAN VERSUS NATURE 

The Los Angeles area provides an outstanding 

and instructive example of the growing importance 

2 

of urban geology. As on the national scene, the importance is the result of the activities of man impinging on the natural environment, but in this megalopolis of southern California both elements are 

notoriously unpredictable. 

Population growth in the Los Angeles area has 

been truly explosive, and the explosion largely uncontained, as any traveler arriving there by air can easily 

judge for himself. From 1950 to 1960, the population 

of the City of Los Angeles grew from nearly 2 million 

to almost 27.! million, an increase of about 25 percent. 

Despite the city's vast geographic extent, which is well 

publicized, the spread of residential subdivisions has 

been so rapid that now only hilly and mountainous terrain remains as the last large area of relatively undeveloped land. Some 60 percent of the city, or roughly 

250 square miles, consists of this hillside area, as it 

is called in the municipal code. It is perhaps 10 percent built upon, with over 60,000 homes, at least 40,000 

of them constructed in the last 10years. City officials 

contend there is room in the hills for 2 million people, 

which also happens to be the population increase anticipated for the city within the next 25 years or so. The 

story of growth is similar for the entire County of Los 

Angeles, where about 40 percent of the people of California live. The County's 1960 population of over 6 

million was exceeded by that of only 8 States. 

The natural setting of the Los Angeles area is 

characterized by rugged· topography, complex and 

highly variable geology, and a semi-arid climate in 

which the rainfall is con c en t r at e d in a few winter 

months. This is a combination that resulted in increasingly serious and widespread engineering problems as urban growth accelerated after World War 

II and thousands of new cuts scarred the hills. Problems of landslides, other slope instabilities, floods, 

and debris flows have tended to dominate, but the total 

list is long and the consequences of neglect are extremely costly. 

The crisis came with the heavy rains of early 1952, 

and thjs crisis turned into a major disaster largely because land developers had generally disregarded things 

geological: Within months the City of Los Angeles had 

enacted the nation's first comprehensive grading ordinance and taken other .steps to remedy the situation 

and prevent its recurrence. The County of Los Angeles 

and other cities and counties within the metropolitan 

area have since followed suit. Grading and subdivision 

regulations specify the requirements for rigorous engineering geology and soil engineering investigations, 

and the regulations are diligently enforced. The relatively minor damage from storms in recent years is 

proof of how well the controls are paying off. 

URBAN ENGINEERING GEOLOGY 

The history ot urban engineering geology in southern California has been brief but eventful. It had its 

real beginnings after the St. Francis dam failure of 

1928, which led to a State law making compulsory the 

geologic investigation of all dam sites. Engineering 

geology played an important role in the planning and 

construction of the Metropolitan Water District's 
famed Colorado River Aqueduct during the 1930's. 

The local profession grew steadily but .very slowly 

until the late 1940's, when the population increase, 

and hence new construction, began to assume massive 

proportions. 

Employment of engineering geologists in all types 

of urban investigations in the Los Angeles area was 

rather impressive by 1953, even before the full effect 

of hillside development controls was felt, but there 

has been a 3-fold increase in the last 10 years, from 

about 50 to about 150 geologists, including some parttimers. A brief summary of present employment in 

the Los Angeles area is pertinent because it is the 

most convincing way of showing the extent to which 

engineering geology is now being used. Keep in mind 

that the following figures are all for this one urban 

area. The summary does not include the many men 

trained as geologists who are now working essentially 

as engineers, even though their geologic background 

commonly was a valuable prerequisite for employment. Nor does it include the numerous engineering 

geologists headquartered in Los Angeles who are not 

engaged in local urban investigations to any appreciable degree. 

Government geologists total about 70. This is 

more than double the number 10 years ago, chiefly 

because of increases in State and county organizations. 

At the Federal level, the largest group consists of 

some 11 geologists of the Corps of Engineers district 

office working mainly on major flood control projects, 

harbor development, and other civilian applications. 

The Geological Survey is represented by 5 members 

of the Engineering Geology Branch, carrying out 3 

projects of detailed areal mapping, much of which is 

being done at the request of and in cooperation with 

the County of Los Angeles. 

The largest of three State agency staffs is that of 

the Department of Water Resources, with 17 engineering geologists engaged in local studies of ground-water 

basin geology and development, waste disposal, saltwater encroachment and contamination, and related 

matters. Nine engineering geologists of the Division 

of Highways are responsible for all local investigation~ of bridge foundations for the extensive freeway 

and State highway _systems, as well as for many route 

surveys and materials investigations. Two geologists 

of the Division of M in e s and Geology, which is the 

State's geological survey, have been doing detailed 

areal mapping under a cooperative agreement with the 

County. 

The County of Los Angeles, which has a civil service payroll of more than 40,000 persons, employs engineering geologists in two of its biggest departments. 

Ten geologists work for the Flood Control District on 

a wide variety of projects about equally divided between the District's two integrated programs of flood 

control and water conservation. Their principal effort currently is with salt-water encroachment barrier projects. The Engineering Geology Section of 

the County Engineer's Department came into existence only 4 years ago, and now has a staff of 5 professionals who are nearly swamped with responsibilities in all geologic aspects of hillside development 

control and major capital projects. These geologists, 

in addition, serve as advisers for most other County 

departments, including the Road Department and the 

Regional Planning Commission. 

Within the City of Los Angeles, several geologists 

are employed by the Public Works Department, mostly 

on hillside investigations, and three geologists work 

for the Dams and Foundations Section of theW ater and 

Power Department, which is the largest municipally 

owned utility in the United States. Recently a geologist position was established within the Department 

of Building and Safety in order to provide needed assistance in control over grading on private property. 

The Metropolitan Water District of Southern California, a public corporation, employs only 1 or 2 geologists at present, though it has had a larger staff in 

the past during periods of major construction programs. 

The field of private utilities is of minor importance locally, with 3 engineering geologists working 

for the Southern California Edison Company. 

The greatest number of geologists is in the field 

of private geological and engineering firms and consultants, for this field has had a tremendous growth, 

chiefly because of the necessity or requirement for 

detailed geologic mapping in connection with hillside 

residential developments. In 1953, perhaps 4 fulltime engineering geologists were in private employ. 

Today there are about 28 in engineeringgeologyfirms 

plus another 20 or so working for soil and foundation 

engineering companies. Noteworthy is an engineering 

geology firm that started in 1959 with 2 partners, now 

has 12 geologists, and recently added a soil engineering group in a reversal of the usualprocedure. Parttime engineering geology consultants have increased 

slightly in number in the past decade, to about 20, but 

they now handle much more work. More than one college faculty member has enough business to keep fulltime assistants occupied. 

LESSONS TO BE LEARNED 

The importance of the Los Angeles experience 

to geologists, engineers, planners, and indeed to the 

public, is that it illustrates the sort of thing that can 

happen and already is beginning to happen elsewhere, 

though on a lesser scale and with variations because 

of differing local conditions. Other urban communities would do well to take note and hopefully avoid 

some of the more violent growing pains in the acquisition and application of geologic information. In particular ,; the experience suggests an ideal sequence of 

mapping investigations to best meet the needs for geologic data in an expanding urban area. 

Firstr and an absolute essential, is modern general-purpose mapping of quadrangles or other large 

areas, such as is undertaken byFederalandState surveys. Where possible, this should precede urban development so that the maps can serve as guides for 

land planning and zoning, and provide background for 

more-detailed local studies. The mapping of suburban 

fringe areas before the central city generally will meet 

greater needs first and take advantage of better exposures. The 7M-minute, 1:24,000-scale (i.e., 1 inch 

equals 2,000 feet) topographic maps are becoming the 
standard base for urban planning activities throughout 

the country, and thus are also the most appropriate 

base for general geologic mapping of urban areas. 

However, in some urban areas geologic complexities 

may make desirable initial large-scale mapping on an 

enlarged base. 

The most useful general-purpose maps for urban 

development are those that emphasize geologic processes and characteristics of geologic materials that 

are significant to land use and civil engineering. But 

even where such emphasis is lacking, valuable guidance 

can be derived from interpretations of the basic geologic data. 

The second stage in the mapping sequence consists 

of larger scale and commonly special-purpose mapping 

of selected areas. Both the County and the City of Los 

Angeles have recognized the need for maps at a scale 

of about 1 inch equals 400 feet in areas where landslides are prevalent and where no geologic maps were 

available at scales larger than 1 :24,000. As part of the 

cooperative program between the County and the State 

Division of Mines and Geology, the broad coastal peninsula of Palos Verdes Hills recently was mapped at 

a scale of 1 inch equals 200feet, with subsequent compilation at 1 inch equals 400 feet. This is an area of 

approximately 26 square miles. The assembled field 

maps, properly fitted together, would measure about 

8 by 12 feet! Geologists of the City of Los Angeles 

have embarked on an ambitious program of mapping 

some 80 square !lliles of hilly and mountainous terrain 

on new photogrammetric base maps at a scale of 1 inch 

equals 400 feet. Such activities are by no means limited to governmental surveys. Private engineering 

geology firms have done extensive mapping at comparable scales for private developments covering up 

to tens of thousands of acres. 

The third stage in the mapping sequence, and the 

one involving by far the greatest number of geologists, 

consists of extremely detailed investigations, chiefly 

for individual hillside subdivisions or specific engineering projects. A common scale for tentative tract 

maps is 1 inch equals 100 feet, and for final grading 

plans 1 inch equals 40 feet. Most such mapping is for 

private development and is done by geologists in engineering and consulting firms. 

MEETING THE NATIONAL NEED FOR 

URBAN GEOLOGIC INFORMATION 

The population figures for the United States show 

that urban growth, with its Pandora's box of planning 

and engineering problems, is not p e c u 1 i a r to Los 

Angeles. It is a nationwide phenomenon. And so also 

the need for urban geologic information, both basic and 

specialized, is nationwide. Much can and should be 

done to take full advantage of such geologic data as 

are already available in published and unpublished 

form, but for most urban areas these will afford at 

best no more than an interim and partial solution. 

New York was the first and still is about the 

only large city in the nation with anywhere near adequate engineering geology information. Most metropolitan areas of the United States desperately need 

new, detailed mapping, and this can only be achieved 

through a greatly magnified engineering geology effort 

involving municipal, county, and State agencies and 

private firms, as well as our universities and colleges. 

The master key to real progress belongs to the local 

governments. They can provide the greatest stimulus 

for urban geologic investigations, and they are in the 

best position to insure that the results are applied for 

the maximum benefit of their citizens. Cities and 

counties can use the geologic information not only 

in the formulation of long-range policies and plans, 

but in the day to day applications that are possible 

with continuity of local operation. 

The recent history of the geological profession 

in Los Angeles and in a number of other cities fosters optimism about the future job outlook for welltrained engineering geologists interested in urban 

work. The major emphasis must always be on quality 

rather than quantity, however, because this is work 

that deserves and demands the best talents. Many of 

our academic institutions would do well to reexamine 

their curricula with a view to improving the capabilities of their graduates for this field of specialization. 

The U. S. Geological Survey has been mapping 

cities for many years as part of its national mapping 

responsibility. The 1902 folio of the New York metropolitan area was a notable early effort. Most of 

the older maps, however, are no longer adequate to 

meet modern requirements for more detailed, specialized, and up-to-date information. In its limited 

program of urban geology studies, the Geological 

Survey hopes to encourage by example the greater use 

of engineering geology in urban areas, and to educate 

public agencies and private concerns in the needs and 

applications of this field to the end that they will develop their own capabilities. 

Mapping and related research by the Geological 

Survey in urban areas is intended to provide general 

background for more detailed site investigations. Individual projects tend to emphasize different aspects 

of the geology, depending on the loeal situation. Studies 

by the Engineering Geology B r an c h are currently 

underway in the following metropolitan areas: Boston, 

Mass.; Washington, D. C.; Great Falls,Mont.; Rapid 

City, S. D.; Omaha-Council Bluffs, Nebr.-Iowa; Salt 

Lake City, Utah; Denver and Pueblo, Colo.; Seattle, 

Wash.; and San Francisco-Oakland, San Mateo-Palo 

Alto, and Los Angeles, Calif. Studies have been completed in recent years in Anchorage, Alaska, Knoxville, Tenn.; and Portland, Oreg., and the reports 

have been published. 

The problems of urban growth a.t e a tremendous 

challenge. Planners and engineers need all the help 

they can get to meet the challenge most effectively. It 

is time geologists fully appreciated that a fundamental 

part of this help must come from their own ranks. The 

challenge to the geological profession is actually the 

more urgent because much of the geologist' work 

should be completed before that of the planners and 

engineers begins. In short, this is a time of opportunity but also a time for responsibility. We have an 

obligation as scientists, as educators, and as good 

citizens to see that the benefits of geologic information are brought to bear as widely and fully as possible 

in the solution of problems of urban growth.