U.S. DEPARTMENT OF THE INTERIOR

U.S. GEOLOGICAL SURVEY

DIGITAL COMPILATION OF "PRELIMINARY MAP OF 

LANDSLIDE DEPOSITS IN SANTA CRUZ COUNTY, 

CALIFORNIA, BY COOPER-CLARK AND ASSOCIATES, 

1975": A DIGITAL MAP DATABASE

by

Sebastian Roberts1 and Andrew D. Barron2

with a preface by

Earl E. Brabb1

 and Richard J. Pike1

Open-File Report 98-792

1998

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm 

names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 

This database, identified as ’Preliminary Map of Landslide Deposits in Santa Cruz County, California: 

A Digital Map Database’, has been approved for release and publication by the Director of the USGS. 

Although this database has been reviewed and is substantially complete, the USGS reserves the right 

to revise the data pursuant to further analysis and review. This database is released on condition that 

neither the USGS nor the U.S. Government may be held liable for any damages resulting from its use.

1) U.S. Geological Survey, Menlo Park, CA

2) presently at Pacific Gas and Electric Company
DIGITAL COMPILATION OF "PRELIMINARY MAP OF 

LANDSLIDE DEPOSITS IN SANTA CRUZ COUNTY, 

CALIFORNIA BY COOPER-CLARK AND ASSOCIATES, 

1975": A DIGITAL MAP DATABASE

 by

Sebastian Roberts and Andrew D. Barron

with a preface by

Earl E. Brabb and Richard J. Pike

ABSTRACT

A 1:62,500-scale black-and-white map identifying some 2,000 landslides of various types 

in Santa Cruz County, California, has been converted to a digital-map database that can be 

acquired from the U.S. Geological Survey over the Internet or on magnetic tape.

PREFACE

The effort toward a landslide inventory of Santa Cruz County began about 1972 when 

Walter Monasch, then Planning Director for the county, saw a landslide inventory and other 

hazard maps prepared for San Mateo County as part of a pilot program underway by the U.S. 

Geologic Survey (USGS) for the nine counties surrounding San Francisco Bay. He asked if the 

USGS would prepare similar maps for his county so that he could respond to a new State of 

California requirement that geologic hazards be considered in the seismic safety element of the 

general plan for all cities and counties. When informed that the USGS did not have the manpower 

to comply with his request, he asked if the USGS would supervise the work of consultants to 

prepare a landslide inventory, a fault map, and a map showing areas that might liquefy during an 

earthquake− providing that the County fund this project. The USGS agreed to find the consultants 

to do the work. N. Timothy Hall was engaged to prepare the fault map, William Dupré the 

liquefaction map, and Cooper-Clark and Associates the landslide inventory. Earl E. Brabb was 

assigned by the USGS to monitor the work. All of the finished maps were added to the seismic 

safety element of the general plan adopted by the Santa Cruz County Board of Supervisors on 

August 26, 1975.

The formal citation for the landslide map is: Cooper-Clark and Associates, 1975, 

Preliminary map of landslide deposits in Santa Cruz County, CA, Planning Department, 1 sheet, 

map scale 1:62,500.

Although the information in this database has not been updated or amended beyond that in 

Cooper-Clark and Associates (1975), it is being released in digital form because it is the only 

systematic landslide-inventory that exists for Santa Cruz County. Users are cautioned that these 

25- to 30-year-old data have shortcomings in addition to the several caveats cited in the original 

map text. Information on the slope-failure hazard is incomplete. Landslides occurring in the 

County after 1970 (date of the latest airphotos used in the 1975 compilation), particularly during 

the severe winters of 1982 (15 fatalities; Cotton, 1982), 1983, and 1998, are not recorded here. 

2
The January 3-5, 1982, storm alone triggered hundreds of debris flows across the County (Ellen 

and others, 1997), and scores of landslides of various types occurred during the 1997-98 El Niño 

causing $9.3 million in damages (Schuster and others, 1998). A few post-1970 maps at medium 

scale are listed below; detailed mapping by private consultants is not cited. Finally, many 

locations in Santa Cruz County that might be susceptible to slope-failure are indicated in a recent 

terrain-based mathematical model that predicts source areas for debris flows (Ellen and others, 

1997). 

This report is organized as three parts. The first reproduces verbatim the entire explanatory 

text printed on the 1975 Cooper-Clark source map. Part II describes compilation of the 

Cooper-Clark map as a digital database and the conventions adopted in encoding its landslide 

information in a geographic information system (GIS). The final section describes details of the 

digital-map database, its constituent data files, and their computer formats. It further lists the steps 

required to obtain the contents of the landslide-map database from USGS.

 RECENT REFERENCES

Clark, J.C., Brabb, E.E., and McLaughlin, R.J., 1989, Geologic map and structure sections of the 

Laurel 7.5-minute quadrangle, Santa Clara and Santa Cruz Counties, California: U.S. 

Geological Survey Open-File Report No. 89-676, 30 p., map scale 1:24,000.

Cotton, W.R., and Cochrane, D.A., 1982, Love Creek landslide disaster, January 5, 1982, Santa 

Cruz County: California Geology, v. 35, no. 7, p. 153-157.

Ellen, S.D., Mark, R.K., Wieczorek, G.F., Wentworth, C.M., Ramsey, D.W., and May, T.E., 1997, 

Map showing principal debris-flow source areas in the San Francisco Bay region, CA: U.S. 

Geological Survey, Open-File Report 97-745 E.

Manson, M.W., Keefer, D.K., and McKittrick, M.A., 1992, Landslides and other geologic features 

in the Santa Cruz Mountains, California, resulting from the Loma Prieta Earthquake of 

October 17, 1989: Calif. Division of Mines and Geology, Open-File Report 91-05, 45 p., 

15 plates, map scale 1:48,000.

McJunkin, R.D., 1983, Landslides, in Geology of the Big Basin Redwoods State Park, Santa Cruz 

County, California: Calif. Div. Mines and Geology, Open-File Report 84-6SAC, 72 p., 

plate 3, map scale 1:24,000.

McLaughlin, R.J., Clark, J.C., and Brabb, E.E., 1988, Geologic map and structure sections of the 

Loma Prieta 7.5-minute quadrangle, Santa Clara and Santa Cruz Counties, California: U.S. 

Geological Survey Open-File Report No. 88-752, 32 p., map scale 1:24,000.

Schuster, R.L., Baum, Rex, and Godt, J.W.,1998, Map showing locations of damaging landslides 

in Santa Cruz County, California, resulting from 1997-98 El Niño rainstorms: U.S. 

Geological Survey Open-File Report, map scale 1:125,000, in press.

Spittler, T.E., and Harp, E.L., 1990, Preliminary map of landslide features and coseismic fissures 

in the Summit Road area of the Santa Cruz Mountains triggered by the Loma Prieta 

earthquake of October 17, 1989: Calif. Division of Mines and Geology, Open-File Report 

90-6, 3 plates, map scale 1:4800.

3
I.

THE SOURCE MAP

This section is repeated verbatim from the 1975 map by Cooper-Clark and Associates

INTRODUCTION

 PURPOSE AND METHOD

Knowledge of the distribution and type of landslides present in a region is one of the kinds 

of geologic information necessary for more effective land-use planning. This map provides such 

information. It is a preliminary map of known and suspected landslides prepared by stereoscopic 

analyses of high and intermediate level aerial photographs. Although prepared and published 

without the benefit of field checking for accuracy and completeness, this map is useful because it 

has quickly provided needed landslide information for immediate use in making land-use 

decisions.

DEFINITION OF TERMS

Landsliding is commonly defined as the "downward and outward movement of 

slope-forming materials composed of natural rock, soils, artificial fills or combinations of these 

materials" (General Reference No. 1). This map shows landslides that have occurred only in 

natural materials. However, the works of man have very likely contributed to the development of 

at least some of the landslides shown.

Landslides are often classified according to the type of materials involved and the type of 

movement which occurs. On this basis, the principal types of landslides are: (1) falls, (2) slides, 

and (3) flows (see Figures 1 and 2). Combinations of these basic types are classified as "complex" 

landslides.

Landslides may also be classified according to age, which is suggestive of their level of 

activity. On this basis, landslides can be tentatively classified as: (1 ) ancient (static), (2) old 

(dormant), or (3) young (active or recently active). Dormant landslides are not presently active, 

but may reactivate under existing natural slope conditions. In contrast, static landslides require a 

gross disturbance of their slope environment before they will be reactivated. Examples of gross 

disturbances are: substantial ground shaking generated by an earthquake, inappropriate grading in 

a critical portion of the slide, and extensive, prolonged saturation of the slide mass.

Classifications which evaluate the certainty of landslide existence provide a reliability 

rating which is often useful, particularly when landslide identification is based upon aerial 

photographic analyses without an opportunity to field check the accuracy of interpretations. A 

three-part classification is often used, based on the confidence the investigator has in his 

interpretations. The following reliability rating classification is commonly used: (1) definite

landslide, (2) probable landslide and (3) questionable landslide.

4
Figure 1. General morphology of recently active landslides

SUMMARY OF LANDSLIDE CAUSES

Included among the major inter-related factors and processes which contribute to landsliding are:

1. Unfavorable geologic structure 

2. Weakened or unconsolidated soil and rock 

3. High annual rainfall 

4. High groundwater levels 

5. Steeply-inclined slopes and irregular topography 

6. Deep weathering 

7. High rates of differential erosion 

8. Seismic ground shaking

9. Activities of man

The activities of man which can initiate landsliding or reactivate dormant or static landslides 

include the following:

1. Inappropriate or poorly engineered cuts and fills.

2. Deflection or blockage of surface or subsurface drainage.

3. Gross removal of protective vegetative cover.

4. Increase in soil and rock moisture through prolonged or excessive outside domestic 

water usage or extensive use of septic tanks and leach fields.

5. Insufficient maintenance or repair of improvements such as culverts, storm drains, 

gutters, etc.

5
LANDSLIDE CONDITIONS IN 

SANTA CRUZ COUNTY 

DISTRIBUTION

Widespread landslide conditions exist in Santa Cruz County. The most intense conditions 

occur in the mountainous areas in the northern and eastern parts of the County. There is 

substantially less landslide development in the more gently sloping areas in the south and west 

parts of the County.

LANDSLIDE TYPES

Landslides in Santa Cruz County vary widely in dimension, age, type of movement and 

type of material.

Most landslides appear to have moved as slumps, earthflows, or as a combination of these 

movements. (see Figures 1 and 2). In the latter situation, movement initially occurs as a slump. 

Following slumping, movement continues, producing an earthflow, often extending a long 

distance downslope from the original slump (see Figure 1).

Other types of landslide movement which appear to have occurred are block glides, debris 

avalanches, rockfalls and sand flows.

Landslides, which vary in maximum surface dimension from a few feet upwards to a few 

hundred feet, are present throughout most portions of the County. In addition, there are numerous, 

remarkably large landslides in the mountainous portions of the County. The surface dimensions 

of these large landslides range from slightly less than 1000 feet to over 8000 feet. Depths are 

estimated to range from 100 to possibly 400 feet. Several of the larger landslides are located along 

the San Andreas Rift Zone, strongly suggesting a correlation between intense ground shaking and 

massive landslide development. In many cases, smaller slides have developed upon the surfaces 

of the large landslides.

The largest landslides appear to be the oldest. The age range for the origin of these 

landslides is probably several hundreds to several thousands of years. Movements may have 

occurred intermittently since time of origin.

6
Figure 2. Classification of landslides After: Varnes, D.J. 1958, Landslide types and process, In 

Eckel, E.B., ed., Landslide and engineering practice: Highway Research Board Spec. Rep. 29, 

NAS- NRC 544, Washington, D.C.,p. 20-47.

LANDSLIDE ACTIVITY AND RATES OF MOVEMENT

Most landslides observed in the aerial photographs do not appear to be grossly active. 

However, observations for slide activity in aerial photographs can be deceptive. For example, a 

large, old landslide which appears dormant or static may have an annual average rate of movement 

that amounts to a few inches. This movement would not be sufficient to show surface distress 

observable in aerial photographs. Therefore, when the activity of a slide is important, detailed 

geologic investigations, including subsurface exploration, should be undertaken for activity 

determination.

Recently active landslides in the County which can be identified in aerial photographs are 

those which have undergone rapid movement (those labeled R on the map see map symbols 

below). These are classified as debris avalanches, or debris flows (see Figure 2). They leave a 

well-defined, readily discernible slide track, or scar from which the slide debris was rapidly 

evacuated. Slides of this type have developed on steep canyon walls. Movement appears to have 

involved only surficial materials or possibly highly weathered bedrock. They are relatively long 

and narrow. The length of the slides and steepness of slopes suggest very rapid movement and a 

fluid condition of the slide material. Because these slides generally occur without forewarning, 

and move with rapidity, they impose a risk to life not normally associated with slower moving 

slides such as earthflows and slumps.

7
MAP PREPARATION

METHOD

Landslides were identified solely by the stereoscopic examination of vertical black and 

white aerial photographs. Both intermediate and high-level photographs were used. Difficult and 

complex areas were reviewed by two and in some cases, three interpreters using both high and 

intermediate-level photographs to develop the best opinion of existing landslide conditions.

AERIAL PHOTO SCALES AND FLIGHT DATES

The following aerial photographs were used in map preparation:

1. U.S. Soil Conservation Service

 Scale: 1:20,000

 Flight Date: 1963

2. U.S. Geological Survey

 Scale: 1:30,000 

 Flight Date: 1967 ,68

3. U.S. Geological Survey

 Scale: 1 :80,000 

 Flight Date: 1970

REGIONAL GEOLOGY

Regional geologic maps (Brabb, 1970; Clark, 1966, 1970a, 1970b; and Farrington, 1974) 

were reviewed to supplement interpretations.

 MAP RELIABILITY

Numerous factors affect the reliability of interpreting landslides from aerial photographs. 

These include:

1. Scale of maps and photography

2. Date(s) of photography 

3. Degree and extent of forest cover

4. Age and activity of landslides

5. Degree and extent of urbanization 

6. Problems of interpretation 

7. Skill and experience in aerial photo interpretation

SCALES OF MAP AND PHOTOGRAPHY

Most landslide deposits less than about 50 feet in maximum dimension are not shown 

because they are too small to be identified on the photographs used (1963, 1 " = 1670’).

8
DATES OF PHOTOGRAPHY

Most of the landslide deposits shown on this map were interpreted from aerial photographs 

taken in 1963 and in 1970. Supplemental interpretations were also made from photographs taken 

in 1967 and 1968. In some areas within the county, particularly in the Santa Cruz-Rio Del Mar, 

Felton-Boulder Creek and Scotts Valley areas, pre-1963 urbanization may have obscured some 

landslides. These landslides would not be identifiable. Also, some small landslides may have 

formed since 1963 which would not be visible in the higher-level 1970 photographs. Such slides 

would also not be delineated. However, since urban areas represent a small percentage of the total 

County area and since most slides formed prior to 1963, the map reliability is not substantially 

affected by photography dates.

FOREST COVER

The degree and extent of forest cover significantly affects the reliability of landslide 

interpretations. This is particularly the case with smaller (less than 50 feet in maximum 

dimension), older landslides whose landform is obscured by dense forest cover. Approximately 

75 percent of the County is mantled by moderate to dense forest cover. This condition is reflected 

on the landslide map by a relatively large percentage of landslides which are classified as being 

"questionable" (see map symbols below).

AGE AND ACTIVITY OF LANDSLIDES

Recently active, well-defined landslides with surface dimensions greater than 50 feet are 

usually discernible in aerial photographs of the scale used in this investigation. Older, inactive or 

slowly moving landslides, which are deeply eroded and obscured by forest cover are more difficult 

to observe unless they have very large dimensions. This condition is also reflected on the landslide 

map by a relatively large percentage of landslides which are classified as being questionable.

PROBLEMS OF INTERPRETATION

Mapping of landslide deposits by photo interpretation presents a number of difficult 

problems, some of which can only be resolved through extensive field checking. Problems that are 

especially difficult include: (1) the distinction of terrace-shaped slump deposits from alluvial 

terrace deposits adjacent to stream courses; (2) the recognition of landslide deposit boundaries that 

have been modified by natural processes and are no longer well-defined− whereas the upslope 

boundary is commonly defined by an easily recognized scarp, the toe or downslope boundary is 

often poorly defined and difficult to locate exactly; (3) the recognition of unslid masses of bedrock 

surrounded by landslide deposits; (4) the distinction of irregular or hummocky topography caused 

by variations in the erosional resistance of bedrock from that caused by landslide activity; and (5) 

the distinction between steep arcuate scarps at the upper slope caused by differential erosion of 

relatively resistant, generally flat-lying beds from similar scarps caused by landslide movement.

SKILL AND EXPERIENCE IN INTERPRETATION

Reliability of interpretations can be affected by the skill and experience of the aerial photo 

interpreters. Interpretations for this map were made by personnel with 5 to 10 years of aerial photo 

interpretation experience. The map, therefore, reflects the current state-of-the-art regarding 

9
interpretation of landforms of landslide origin from aerial photographs.

IMPROVING MAP RELIABILITY

The reliability of this landslide map can be improved by integrating it with other landslide 

data. Such data would be from site specific studies conducted by consultant firms, landslide repair 

records from public works agencies, subregional landslide maps prepared by students and/or 

faculty of Bay Area universities, and by field checking the map for accuracy and completeness.

MAP USE AND LIMITATIONS

USE

This map is primarily intended for advance planning purposes. It provides an early 

indication of possible slope stability problems associated with areas which may be subject to 

various types of proposed improvements. The map can also be used to make relative comparisons 

between alternative sites for feasibility purposes and for the scoping of needed sites specific 

stability investigations. It can also be used as a basis for developing requirements for 

predevelopment investigations which must be met as a requisite to development.

When this map is used in conjunction with available Countywide geologic and slope maps, 

it is possible to analyze and evaluate the susceptibility of various areas within the County with 

respect to future landslide development. Such evaluations should only be undertaken by qualified 

geotechnical personnel.

LIMITATIONS

This map is intended for regional landuse evaluations and decisions. It is not intended for 

detailed slope stability evaluations of individual sites. Such information must be developed during 

detailed site specific engineering and geologic studies.

This map is no more detailed than the aerial photographs and maps used. For this reason, 

small localized slides may be present which are not shown on the maps and some larger slides may 

not be shown because they are obscured by dense forest cover.

GENERAL REFERENCES ON LANDSLIDE DEPOSITS 

1. Eckel, E. B., ed., 1958, Landslide and engineering practice: Highway Research Board Spec. 

Rept. 29, NAS/NRC 544, Washington, D.C., 232 p.

2. Flawn, P.T., 1970, Environmental geology; conservation, landuse planning, and resource 

management: New York, Harper & Row, 313 p.

3. Sharpe, C.F.S., 1960, Landslides and related phenomena: Paterson, N.J., Pageant Books, 137 p.

4. Terzaghi, Karl, 1950, Mechanism of landslides, In Paige, S.M., Chm., Application of geology 

to engineering practice (Berkey volume): New York, Geol. Soc. America, P. 83-123.

5. Zaruba, Quido, and Mencl, Vojtech, 1969, Landslides and their control: Amsterdam, Elsevier 

Pub. Co., 205 p.

10
SELECTED REPORTS ON LANDSLIDE DEPOSITS AND REGIONAL 

GEOLOGY IN SANTA CRUZ AREA

Brabb, E.E., 1960, Geology of the Big Basin area, Santa Cruz Mountains, California: Stanford 

University, unpublished Ph.D. thesis, 192 p.

Brabb, E.E., compiler, 1970, Preliminary geologic map of the central Santa Cruz Mountains, 

California: U.S. Geological Survey Basic Data Contribution no. 6.

Brabb, E.E., and Pampeyan, E.H., 1972, Preliminary map of landslide deposits in San Mateo 

County, California: U.S. Geological Survey Miscellaneous Field Studies Map MF344, 

scale 1 :62,500 (Basic Data Contribution no. 42).

Clark, J.C., 1966, Tertiary stratigraphy of the Felton-Santa Cruz area, Santa Cruz Mountains, 

California: Stanford University, unpublished Ph.D. thesis, 184 p.

Clark, J.C., 1970a, Geologic map of the southwestern Santa Cruz Mountains between Año Nuevo 

Point and Davenport, California: U.S. Geological Survey Open File Map.

Clark, J.C., compiler, 1970b, Preliminary geologic and gravity maps of the Santa Cruz-San Juan 

Bautista area, Santa Cruz, Santa Clara, Monterey, and San Benito Counties, California: 

U.S. Geological Survey Open File Map.

Cummings, J.C., Touring, R.M., and Brabb, E.E., 1962, Geology of the northern Santa Cruz 

Mountains, California: California Division of Mines and Geology Bulletin 181, p. 

179-220.

Farrington, R.L., 1974, Active fault and landslide hazards along the San Andreas fault zone, 

southeast Santa Cruz County, California: University of California, Santa Cruz, 

unpublished Ph.D. thesis.

II.

DIGITAL COMPILATION

INTRODUCTION

The landslide deposit database was compiled using version 7.1.1 of ARC/INFO, a 

commercial geographic information system, or GIS (Environmental Systems Research Institute 

[ESRI], Redlands, California) on a UNIX computer using the menu interface ALACARTE 

(versions 1 through 3.1: Fitzgibbon and Wentworth, 1991; Fitzgibbon, 1991; Wentworth and 

Fitzgibbon, 1991). 

 The digital compilation was derived from linework inked directly by the authors on 17 

USGS mylar greenline 7.5-minute (1:24,000-scale) quadrangle maps that cover Santa Cruz 

County. The inked linework for each source map was scanned (800 dots per inch), converted 

from raster to vector form, imported into ARC/INFO, and hand edited and combined into a single 

digital file. Small adjustments were made to fit lines across quadrangle boundaries, but larger 

misfits were retained. The base map for the landslide data includes topography, drainage, and 

culture at a scale of 1:125,000. These base layers were derived from USGS Bay Region 

Topographic Sheets (Aitken 1997).

The boundary of Santa Cruz County was added to the database to delineate the area of 

11
detailed mapping inside the county, This county line was derived from Wentworth 1997. Any 

landslides mapped outside the county boundary were deleted and are not included in this map 

database. The 17 constituent USGS quadrangles are: Mindego Hill, Cupertino, Franklin Point, Big 

Basin, Castle Rock Ridge, Los Gatos, Año Nuevo, Davenport, Felton, Laurel, Loma Prieta, Mount 

Madonna, Santa Cruz, Soquel, Watsonville West, Watsonville East, and Chittenden. The Moss 

Landing quadrangle was omitted from the database because the authors did not map any landslide 

deposits within its boundary.

LANDSLIDE-DEPOSIT UNITS

The spatial database uses two different symbols to represents landslide deposits in two 

separate data layers. All landslides larger than 500 feet in maximum dimension are delineated by 

polygons enclosing their approximate boundaries. Each landslide with a maximum dimension of 

50 to 500 feet is represented in the database by a point, which is printed as an arrow on the 

landslide deposit map and can be plotted from the Postscript and PDF plotfiles included with the 

database. This arrow points in the direction of downslope movement and is centered over the point 

representing the location of the deposit. Although the smaller landslides range in size from 50 to 

500 feet, the arrow symbol for each of these slides is the same size and measures about 180 feet . 

The primary landslide identifier is a character string in the field PTYPE (polygon type) in the large 

landslide data layer and PTTYPE (point type) in the small landslide data layer.

 Because landslides in this database were identified via analysis of aerial photographs 

without an opportunity to field check the resulting map, the values in the PTYPE and PTTYPE 

fields classify the degree of confidence the author has in his interpretations. The values for this 

field range from Definite to Questionable. In both the Postscript and PDF plot files, large 

landslide polygons are color coded according to this classification, and the small landslides have 

these classifications printed at the head of each arrow as annotation.

Table 1. General PTYPE and PTTYPE Categories

Descriptions of landslide categories are modified from the Cooper-Clark Landslide Map Explanation.

D - definite landslide deposit

P - probable landslide deposit

? - questionable landslide deposit

<no value> - landslide without any attribute

R - a modifier added to one of the above values for landslide features that strongly suggest 

a rapid rate (several feet per second to over 100 feet per second) of landslide movement.

SPATIAL RESOLUTION

Uses of this digital map should not violate the spatial resolution of the data. Although the 

digital form of the data removes the physical constraint imposed by the scale of a paper map, the 

detail and accuracy inherent in map scale are also present in the digital data. Because this database 

was compiled from maps at a scale of 1:24,000, higher-resolution information is not present. 

Enlargement of the database to scales larger than 1:24,000 will not yield greater real detail, 

although it may reveal fine-scale irregularities below the intended resolution of the database. 

Similarly, where this database is used in combination with other data of higher resolution, the 

resolution of the combined output will be limited by the lower resolution of this data. 

12
SPECIFICS OF THE LANDSLIDE-DEPOSIT DATABASE

The landslide-deposit spatial database itself consists of various data layers each with the 

naming convention pf-extn. The abbreviation <pf> represents the quadrangle prefix, and the 

abbreviation <extn> is a data layer extension (suffix). The various data layers are described in 

Table 2 below. The map layer is stored in UTM projection (zone 10) (see Table 3), and projection 

files are included to convert between that and the state plane projection. Digital tics define a 7.5 

minute grid of latitude and longitude (see 7.5 MINUTE QUADRANGLE GRID, below). The 

contents of the map database are described in terms of the lines, areas, and points that compose it. 

The terms in Table 4 describe the database fields.

Table 2. Data Layers

DATA LAYER NAME DESCRIPTION

pf-slid_um polygons for large landslides,

fault scarps, map boundaries, 

coastal water boundary, county boundary

pf-smls_um point features for small landslides.

There is no cu-smls_um layer.

pf-anno_um annotation showing landslide type on large

landslides, arrow showing downslope

 movement on large landslides.

The cu-anno_um layer does not contain

downslope movement arrows.

Table 3. Map Projection

projection UTM (universal transverse mercator)

units meters

zone 10

datum NAD27

spheriod CLARKE 1866

Table 4. Field Definition Terms

ITEM NAME name of the database field (item) 

WIDTH maximum number of digits or characters stored

OUTPUT output width

TYPE B- binary integer, F- binary floating point number, N- ASCII 

floating point number, I- ASCII integer, C- ASCII character string

N.DEC number of decimal places maintained for floating point numbers

13
Lines - Database lines (arcs) are recorded as strings of vectors with characteristics that are 

described in the arc attribute table (see Table 5). In the pf-slid_um map layer they define the 

boundaries of the landslide units, topographic escarpments, the boundary of the coastline, the map 

and internal sheet boundaries, scratch boundaries, and the boundary of Santa Cruz County. In the 

pf-anno_um layer they define the arrows showing downslope movement of large landslides. 

These distinctions are recorded in the LTYPE database field according to the line types listed in 

Table 6. Please note that the lines representing topographic escarpments have endpoints that are 

dangling (i.e. they do not complete an enclosed polygon) and will be displayed as errors with the 

node errors option in ARC INFO.

Table 5. Content of the Arc Attribute Table 

(PF-SLID.AAT & PF-ANNO.AAT PF = quadrangle prefix)

 ITEM NAME WIDTH OUTPUT TYPE N.DEC 

FNODE# 4 5 B starting node of arc (from node)

TNODE# 4 5 B - ending node of arc (to node)

LPOLY# 4 5 B polygon to the left of the arc

RPOLY# 4 5 B - polygon to the right of the arc

LENGTH 4 12 F 3 length of arc in meters

PF-SLID# 4 5 B - unique internal control number

PF-SLID-ID 4 5 B - unique identification number

LTYPE 35 35 C - line type

Table 6. Line Types Recorded in the LTYPE Field

The line types are ALACARTE style types that correlate with geologic line symbols in the 

ALACARTE line set GEOLOGY.LIN according to the ALACARTE lines lookup table 

GEOLINE.LUT.

 LINE TYPE DESCRIPTION

 contact, certain arcs delineating large landslide polygons

 topographic escarpment inferred main scarp on large landslides

 arrow, certain arrow showing downslope movement on large landslides

 county boundary Santa Cruz County boundary

 scratch boundary questionable boundary added during digital compilation

 map boundary quadrangle and sheet boundary

 water boundary water boundary on the coastline

Areas - Large landslide units (maximum dimension greater than 500 feet) are recorded as 

vector polygons with characteristics that are described in the polygon attribute table (see Table 7). 

The primary unit identifier is PTYPE. 

14
Table 7. Content of the Polygon Attribute Table 

(PF-SLID.PAT PF = quadrangle prefix)

 ITEM NAME WIDTH OUTPUT TYPE N.DEC

 AREA 4 12 F 3 area of polygon in square meters

PERIMETER 4 12 F 3 length of perimeter in meters

PF-SLID# 4 5 B - unique internal control number

PF-SLID-ID 4 5 B - unique identification number

PTYPE 35 35 C - landslide category

Points - Small landslide units (maximum dimension 50 to 500 feet) are recorded as point 

features in ARC/INFO. These point features are plotted as arrows showing the direction of 

downslope movement and are centered over the location of the slide. Although the slides range in 

length from 50 to 500 feet, all arrows have the same length of approximately 180 feet when 

plotted. In both the Postscript and PDF plot files, the value for PTTYPE is printed as an annotation 

at the head of each landslide arrow. 

Table 8. Content of the Point Attribute Table 

(PF-SMLS.PAT PF = quadrangle prefix)

 ITEM NAME WIDTH OUTPUT TYPE N.DEC

 AREA 4 12 F 3 area of polygon in square meters

 PERIMETER 4 12 F 3 length of perimeter in meters

 PF-SMLS# 4 5 B - unique internal control number

 PF-SLID-ID 4 5 B - unique identification number

 PTTYPE 35 35 C - landslide category

 STRIKE 3 3 I - direction of downslope movement in degrees

 

REFERENCES CITED

Aitken, D.S., 1997, U.S. Geologic Survey Bay Region topographic Sheets 1:125,000 1970. U.S. 

Geological Survey, Open-File Report 97-500.

Fitzgibbon, T.T., 1991, ALACARTE installation and system manual (version 1.0): U.S. 

Geological Survey, Open-File Report 91-587 B.

Fitzgibbon, T.T., and Wentworth, C.M., 1991, ALACARTE user interface - AML code and 

demonstration maps (version 1.0): U.S. Geological Survey, Open-File Report 91-587 A.

Wentworth, C.M., 1997, General Distribution of Geologic Materials in the San Francisco Bay 

Region, California 1: 125,000. A Digital Map Database: U.S. Geological Survey, 

Open-File Report 97-744

Wentworth, C. M., and Fitzgibbon, T.T., 1991, ALACARTE version 1 through 3.1: U.S. 

Geological Survey, Open-File Report 91-587 C

15
.

III.

THE DIGITAL DATABASE

INTRODUCTION

This report consists of a digital map database, a digital map image derived from it entitled 

"Preliminary Map of Landslide Deposits in Santa Cruz County, California: A Digital Map 

Database", and supporting files. The map is at a scale of 1:62,500. The report is stored as several 

digital files, for the spatial data both ARC export (uncompressed) and ARCVIEW shape formats, 

and for the map image both Postscript and PDF formats. The exported ARC coverages lie in UTM 

zone 10 projection and the shape versions are coded in decimal degrees. This pamphlet, which 

only describes the content and character of the digital map database, is included as postscript. PDF, 

and ASCII text files and is also available on paper as USGS Open-File Report 98-792. A plotted 

copy of the map can be ordered from a USGS Earth Science Information Center or by phone at 

1-800-USMAPS. Any or all of the digital files can be obtained over the Internet or by magnetic 

tape copy, as described at the end of this section. 

The full versatility of the spatial database is realized by importing the ARC export files into 

ARC/INFO or an equivalent GIS. Other GIS packages, including MapInfo and ARCVIEW, can 

use either the ARC export or shape files. The Postscript map image can be used for viewing or 

plotting in computer systems with sufficient capacity, and the considerably smaller PDF image file 

can be viewed or plotted in full or in part from Adobe ACROBAT software running on Macintosh, 

PC, or UNIX platforms.

DATABASE CONTENTS

The nine sets of digital files comprising the database, are encoded in more than one format. 

The names of the files are unique designators based on the report identifier, of98-792, followed by 

part numbers (i.e. 3 through 6 below) and an extension indicating file type. Some of the files have 

been bundled using the tar (UNIX Tape Archive) utility (.tar extension). All of the larger files 

have been compressed with the gzip utility, indicated by the .gz extension. The files and their 

identities are as follows:

 1. Revision List: A list of the parts of the report and at what version number of the report each 

was last revised (if at all) followed by a chronologic list that describes any revisions (see 

REVISIONS, below).

 of98-792revs_1a.txt ASCII file 

 2. Open File Text: The open-file pamphlet (this text), which describes the database and how 

to obtain it. 

of98-792_2a.txt ASCII file 

 of98-792_2b.ps Postscript file 

of98-792_2c.pdf PDF file

16
 3. Database for Large Landslide Deposits: ARC export coverages for each quadrangle 

containing both lines and polygons. Import aml will name these coverages pf-slid_um. (pf 

is the quadrangle prefix)

FILE NAME QUADRANGLE NAME

of98-792_3a.e00.gz Mindego Hill

of98-792_3b.e00.gz Cupertino

of98-792_3c.e00.gz Franklin Point

of98-792_3d.e00.gz Big Basin

of98-792_3e.e00.gz Castle Rock Ridge

of98-792_3f.e00.gz Los Gatos

of98-792_3g.e00.gz Año Nuevo

of98-792_3h.e00.gz Davenport

of98-792_3i.e00.gz Felton

of98-792_3j.e00.gz Laurel

of98-792_3k.e00.gz Loma Prieta

of98-792_3l.e00.gz Mount Madonna

of98-792_3m.e00.gz Santa Cruz

of98-792_3n.e00.gz Soquel

of98-792_3o.e00.gz Watsonville West

of98-792_3p.e00.gz Watsonville East

of98-792_3q.e00.gz Chittenden

4. Database for Annotation on Large Landslides and Downslope Movement Arrows: ARC 

export coverages for each quadrangle containing the annotation layer, which consists of 

annotation on the large landslide polygons and arcs representing the arrows on large 

landslide polygons. Import aml will name these coverages pf-anno_um.

FILE NAME QUADRANGLE NAME

of98-792_4a.e00.gz Mindego Hill

of98-792_4b.e00.gz Cupertino

of98-792_4c.e00.gz Franklin Point

of98-792_4d.e00.gz Big Basin

of98-792_4e.e00.gz Castle Rock Ridge

of98-792_4f.e00.gz Los Gatos

of98-792_4g.e00.gz Año Nuevo

of98-792_4h.e00.gz Davenport

of98-792_4i.e00.gz Felton

of98-792_4j.e00.gz Laurel

17
of98-792_4k.e00.gz Loma Prieta

of98-792_4l.e00.gz Mount Madonna

of98-792_4m.e00.gz Santa Cruz

of98-792_4n.e00.gz Soquel

of98-792_4o.e00.gz Watsonville West

of98-792_4p.e00.gz Watsonville East

of98-792_4q.e00.gz Chittenden

5. Database for Small Landslide Deposit: ARC export coverage for each quadrangle 

containing points. Import aml will name these coverages pf-smls_um.

FILE NAME QUADRANGLE NAME

of98-792_5a.e00.gz Mindego Hill

(no Cupertino layer)

of98-792_5c.e00.gz Franklin Point

of98-792_5d.e00.gz Big Basin

of98-792_5e.e00.gz Castle Rock Ridge

of98-792_5f.e00.gz Los Gatos

of98-792_5g.e00.gz Año Nuevo

of98-792_5h.e00.gz Davenport

of98-792_5i.e00.gz Felton

of98-792_5j.e00.gz Laurel

of98-792_5k.e00.gz Loma Prieta

of98-792_5l.e00.gz Mount Madonna

of98-792_5m.e00.gz Santa Cruz

of98-792_5n.e00.gz Soquel

of98-792_5o.e00.gz Watsonville West

of98-792_5p.e00.gz Watsonville East

of98-792_5q.e00.gz Chittenden

6. Line and polygon ARCVIEW shape files bundled as one tar file. When opened, the tar file 

yields:

- line files pf-arc.dbf, pf-arc.shp, and pf-arc.shx

- polygon files pf-poly.dbf, pf-poly.shp, and pf-poly.shx 

-line files pf-anno.dbf, pf-anno.shp, and pf-anno.shx

-point files pf-smls.dbf, pf-smls.shp, and pf-smls.shx 

Note: The annotation in the pf-anno_um data layer is not included in this format because 

ARCVIEW shape files do not support annotation. of98-792_6b.tar.gs does not contain 

pf-anno or pf-smls data layers.

18
FILE NAME QUADRANGLE NAME

of98-792_6a.tar.gz Mindego Hill

of98-792_6b.tar.gz Cupertino

of98-792_6c.tar.gz Franklin Point

of98-792_6d.tar.gz Big Basin

of98-792_6e.tar.gz Castle Rock Ridge

of98-792_6f.tar.gz Los Gatos

of98-792_6g.tar.gz Año Nuevo

of98-792_6h.tar.gz Davenport

of98-792_6i.tar.gz Felton

of98-792_6j.tar.gz Laurel

of98-792_6k.tar.gz Loma Prieta

of98-792_6l.tar.gz Mount Madonna

of98-792_6m.tar.gz Santa Cruz

of98-792_6n.tar.gz Soquel

of98-792_6o.tar.gz Watsonville West

of98-792_6p.tar.gz Watsonville East

of98-792_6q.tar.gz Chittenden

7. Supporting files for ARC/INFO use, bundled as one tar file. When opened, the tar file yields:

- utm2sp.prj and sp2utm.prj: These are projection files to convert between the UTM zone 

10 projection of the database and state plane projection.

- import.aml: This is an ASCII script written in Arc Macro Language for converting the 

ARC export files into usable coverages and INFO files that are assigned standard names 

(see IMPORTING THE ARC EXPORT FILES). 

of98-792_7a.tar

 8. Quadrangle Index Database: The data files representing lines and polygons of the 

quadrangle index (ARC export and ARCVIEW shape format). The ARC version also 

includes quadrangle names as annotation.

of98-792_8a.e00.gz ARC export coverage containing lines, polygons, and annotation. 

Import.aml will name this coverage cc-index_um.

of98-792_8b.tar.gz Line and polygon ARCVIEW shape files bundled as one tar file. 

When opened, the tar file yields:

- line files grdlns.dbf, grdlns.shp, and grdlns.shx

- polygon files grdpys.dbf, grdpys.shp, and grdpys.shx

19
 9. Plot File for the Map: Landslide Deposits in Santa Cruz County which measures 50 by 36 

inches when plotted.

of98-792_9a.ps.gz Postscript file ( 27 MB compressed to 5.8 MB)

of98-792_9b.pdf PDF file (7.8 MB)

REVISIONS

Changes to any parts of the report (the numbered items described above and listed in the 

revision list of98-792revs_a.txt) may be made in the future if needed. These could involve, for 

example, fixing files that don’t work, correcting or adding landslide details, or adding new file 

formats or other components. Major revision of the basic landslide information would result in a 

new report.

The report begins at version 1.00. Any revisions will be noted in the revision list and will 

result in the recording of a new version number for the report. Small changes will be indicated by 

decimal increments and larger changes by integer increments in the version number. Revisions 

will be announced and maintained on the Web page for this report on the Western Region 

Geologic Information Server (see next section).

OBTAINING THE DATA FILES

The database may be obtained in three ways.

1. The simplest way to obtain the database is to download it over the World Wide Web from the 

USGS Western Region Geologic Information Server:

http://wrgis.wr.usgs.gov

From the main page, click on ’Geologic map databases’ under the heading ’Data On-line’; 

next click on ’California’. Scroll down to the listing for this database (Open File Report 98-792) 

and click on the Open-File button, which takes you to the page for this publication. You can also 

go directly to that final page at: 

http://wrgis.wr.usgs.gov/open-file/of98-792

On this page, the several parts of the report in their different file types are separately 

available. Set your Web browser to save to a local disk and click on the appropriate links to 

download the desired files.

2. To download the files from the Internet via anonymous ftp:

ftp wrgis.wr.usgs.gov - make ftp connection with the USGS computer wrgis.

Name: anonymous - enter "anonymous" as your user name.

20
Password: [your address] - enter your own email address as password.

pub/open-file/of98-792 -the subdirectory in which the files from this report are stored

3. To obtain files from the database on magnetic tape, send a blank tape with your request specifying 

the desired files and your return address to:

San Francisco Bay Geologic Materials Database

c/o Database Coordinator 

U.S. Geological Survey

345 Middlefield Road MS 975

Menlo Park, CA 94025

The specified files bundled in a compressed tar file will be returned to you on the tape. The 

acceptable tape types are: 2.3 or 5.0 GB, 8 mm Exabyte tape

OPENING THE DATABASE FILES

Some of the files are packaged as tar files, and the larger files containing the databases and 

images have been compressed with gzip. Thus gzip is required to uncompress the files, and a tar utility 

is required to open the tar files. The necessary utilities are available on-line:

Compressed Gzip Files

Files compressed with gzip (those with a .gz extension) can be uncompressed with gzip. The gzip 

utility converts the compressed file name.gz to its uncompressed equivalent name. The compressed 

file is replaced by the uncompressed file. This utility is free of charge over the Internet at:

 http://w3.teaser.fr/∼jlgailly/gzip

Tar Files (UNIX Tape Archive)

To extract the contents of a tar file, first uncompress it with gzip if the extension is .tar.gz. Once the 

tar extension is exposed, extract the contents with a tar utility. This utility is included in most UNIX 

systems. Tar utilities for PC and Macintosh can be obtained free of charge via the Internet from 

Internet Literacy’s Common Internet File Formats Web Page: 

http://www.matisse.net/files/formats.htm

WinZip

This commercial package runs on PCs and can deal with both gzip and tar files. An evaluation copy of 

WinZip for Windows 3.1, 95 and NT can be downloaded from:

http://www.winzip.com/winzip/: 

21
IMPORTING THE ARC EXPORT FILES 

The ARC export files (__.e00) can be converted to ARC/INFO vector maps (coverages) 

and INFO files by running the import.aml that is included in the database. This will import the 

export files and assign standard names (see below). Run import.aml from the ARC prompt in the 

directory containing the export files:

ARC: &run import.aml - run import.aml 

Note that the arc coverages and separate INFO files will be given standard names:

of98-792_3a.e00 through 

of98-792_3q.e00 (Large Landslide Deposit Database) is named pf-slid_um

of98-792_4a.e00 through

of98-792_4q.e00 (Large Landslide Arrows Database) is named pf-anno_um

of98-792_5a.e00 through

of98-792_5q.e00 (Small Landslide Deposit Database) is named pf-smls_um

of98-792_8a.e00.gz (Quadrangle Index Database) is named cc-index_um

22