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 DuprŽ 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.  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 Ni–o 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 Ni–o 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.







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.













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.











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.

































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.







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').





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
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.









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 A–o 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 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, A–o 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.    



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





	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. 











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

.

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



 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  		A–o 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  		A–o Nuevo

	of98-792_4h.e00.gz		Davenport

	of98-792_4i.e00.gz		Felton

	of98-792_4j.e00.gz		Laurel

	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  		A–o 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.





	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  		A–o 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









 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.

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/:  







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