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# PRELIMINARY SOIL-SLIP SUSCEPTIBILITY MAPS, SOUTHWESTERN CALIFORNIA {#preliminary-soil-slip-susceptibility-maps-southwestern-california .Style1}

*By* D.M. Morton^1^, R.M. Alvarez^1^, and R.H. Campbell^1^

*Digital preparation by* K.R. Bovard^1^, D.T. Brown^2^, K.M. Corriea^1^,
*and* J.N. Lesser^3^

*Prepared in cooperation with*

CALIFORNIA GEOLOGICAL SURVEY

Open-File Report OF 03-17

2003

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 Soil-Slip Susceptibility Maps,
Southwestern California" has been approved for release and publication
by the Director of the USGS.

U.S. DEPARTMENT OF INTERIOR

U.S. GEOLOGICAL SURVEY

^1^U.S. Geological Survey

Department of Earth Sciences

###### University of California

Riverside CA 92521

^2^Department of Earth Sciences

University of California

Riverside CA 92521

^3^U.S. Forest Service

Department of Earth Sciences

University of California

Riverside CA 92521

## TABLE OF CONTENTS

Introduction

General

How to obtain paper plots

Database contents

Data package

Plot package

Other files

Software utilities

How to obtain the digital files

How to extract the soil-slip susceptibility map database from the tar
files

Digital database

Postscript plot files

Portable Document Format (.pdf) files

Digital soil-slip susceptibility map specifications

Digital compilation

Spatial resolution

Map accuracy standards

Database specifics

General

References

## INTRODUCTION

### **General**

Open-file Report 03-17 contains a digital soil-slip susceptibility map
database of southwestern California that includes:

1.  ARC/INFO (Environmental Systems Research Institute,
    [http://www.esri.com]{.underline}) version 8.1 grids of the
    soil-slip susceptibility maps.

2.  Postscript files to plot the soil-slip susceptibility maps on a
    topographic base.

3.  Ascii text files and Portable Document Format (.pdf) files of:

```{=html}
<!-- -->
```
1.  This Readme; includes in Appendix I, data contained in sus_met.txt

2.  The same graphic as plotted in 2 above. Test plots have not produced
    precise 1:100,000-scale map sheets. Adobe Acrobat page size setting
    influences map scale.

```{=html}
<!-- -->
```
4.  Accompanying text that describes the map, the process used to
    produce the map, and its uses.

This Readme file describes the digital data, such as types and general
contents of files making up the database, and includes information on
how to extract and plot the maps and accompanying graphic files.
Metadata information can be accessed at
<http://geo-nsdi.er.usgs.gov/metadata/open-file/03-17>and is included in
Appendix I of this Readme.

## HOW TO OBTAIN PAPER PLOTS

For those having access to large-format plotters such as HP650C, HP755C,
HP2500C, and HP5000, plots may be made directly from the included plot
file.

## DATABASE CONTENTS

The files constituting the soil-slip susceptibility map database of this
Open-file Report are listed below along with the interchange files from
which they are extracted.

### **Data Package**

All files listed below are in compressed tar files (\*.tar.gz, ranging
in size from 0.6 Mb to 10.5 Mb); see section below titled, SOFTWARE
UTILITES.

  -------- ------------------ --------------- ------------ ---------------------
  Plate    Area covered       Compressed tar  ARC/INFO     Contains
  Number                      file            Grid         

  Plate 1  Santa Barbara 100K sbarb_sus.tar   sbarb_sus    Cells with soil-slip
           sheet                                           susceptibility values

  Plate 2  Part of the Los    la_sus.tar      la_sus       Cells with soil-slip
           Angeles 100K sheet                              susceptibility values

  Plate 3  South half of the  sbern_sus.tar   sbern_sus    Cells with soil-slip
           San Bernardino                                  susceptibility values
           100K sheet                                      

  Plate 4  Long Beach 100K    lb_sus.tar      lb_sus       Cells with soil-slip
           sheet                                           susceptibility values

  Plate 5  Santa Ana 100K     sa_sus.tar      sa_sus       Cells with soil-slip
           sheet                                           susceptibility values

  Plate 6  Oceanside 100K     ocs_sus.tar     ocs_sus      Cells with soil-slip
           sheet                                           susceptibility values

  Plate 7  San Diego and      sd_sus.tar      sd_sus       Cells with soil-slip
           eastern part of                                 susceptibility values
           the El Cajon 100K                               
           sheet                                           
  -------- ------------------ --------------- ------------ ---------------------

> The directory, info/, is produced in the process of importing
> interchange files to ARC grids in ARC/INFO. For example the la_sus
> (Los Angeles 30' X 60' quadrangle) info/ directory contains:

+--------------------------------------+-------------------------------+
| ### Feature Attribute Tables         |                               |
+--------------------------------------+-------------------------------+
| Value attribute table                | la_sus.vat                    |
+--------------------------------------+-------------------------------+

### **Plot Package** 

Postscript plot files of the susceptibility maps; please see section
below titled, SOFTWARE UTILITIES for additional information.

+--------------------+---------------------+---------------------------+
| #                  | ### Resultant image | ### Contains              |
| ## Compressed file |                     |                           |
+--------------------+---------------------+---------------------------+
| plate\*.ps.zip     | plate\*.ps          | Postscript plot file of   |
|                    |                     | susceptibility map        |
+--------------------+---------------------+---------------------------+

The Postscript files are compressed using winzip.

The uncompressed Postscript files will plot 1:100,000 scale, full color
soil-slip susceptibility maps of the quadrangles included in the report
on a topographic base. The sheets range from 25 X 36 inches to 41X 36
inches in size. The map sheet has been successfully plotted on
Hewlett-Packard large-format plotters, models HP650C, HP2500C, and
HP5000.

### **Other files**

README.pdf This document

plate\*.pdf Portable Document Format file of the susceptibility map (the
asterisk used here

and in the text that follows is a wildcard meant to represent each of
the seven

soil-slip susceptibility maps included in this database)

text.pdf Portable Document Format file of the accompanying text.

## SOFTWARE UTILITIES

Files which have a .gz file extension were compressed using gzip. Gzip
utilities are available free of charge via the Internet at the gzip home
page, [http://www.gzip.org](http://www.gzip.org/)[.]{.underline} Files
with a .zip file extension were compressed using WinZip, available at
[http://www.winzip.com](http://www.winzip.com/).

The data files are additionally bundled into tar (tape archive) files.
The individual files must be extracted using a tar utility, available
free of charge via the Internet through links on the Common Internet
File Formats page, <http://www.matisse.net/files/format.html>. One such
utility is WinZip, available at
[http://www.winzip.com](http://www.winzip.com/).

## HOW TO OBTAIN THE DIGITAL FILES

The data and plot files, constituting the susceptibility map database of
this Open-file Report may be obtained over the Internet.

-   The files can be obtained via the Web from Western Region Geologic
    Information Server. Go to the web page at
    [http://geopubs.wr.usgs.gov/open-file/of03-17]{.underline} and
    follow the directions to download the files.

## HOW TO EXTRACT THE SOIL-SLIP SUSCEPTIBILITY MAP DATABASE FROM THE TAR FILE

### **Digital database**

> After downloading the files, they must be uncompressed using a gzip
> utility such as gzip itself or WinZip. The data files must then be
> extracted using a tar utility or Winzip.
>
> This process will create a directory such as la_sus/, that will
> contain the ARC/INFO grid and supporting files. When uncompressing the
> files, do not extract them to an existing workspace, as this will
> destroy the pre-existing info directories, coverages and grids. The
> directory should contain the following files:

la_sus/

la_sus ARC/INFO grid

sus.rmp ARC/INFO remap table

/info ARC/INFO info directory

> The remap table (sus.rmp) is provided with each ARC/INFO grid, and is
> identical for each map. The remap table values are used in conjunction
> with colornames.shd (this is a standard ARC/INFO shadeset).
>
> The following are not included in the database tar file, but can be
> downloaded separately.
>
> plate\*.ps.zip
>
> README.pdf
>
> text.pdf
>
> plate\*.pdf

### **Postscript plot files**

> Make an uncompressed file, plate\*.ps (plot of complete map, ranging
> in size from 19 Mb to 75 Mb), by using gzip or winzip utility of
> choice.

### **Portable Document Format (.pdf) files**

> PDF files are not stored as gzip files. They are accessed using Adobe
> Acrobat Reader software, available free from the Adobe website
> [http://www.adobe.com](http://www.adobe.com/). Follow instructions at
> the website to download and install the software. Acrobat Reader
> contains an on-line manual and tutorial.

## DIGITAL SUSCEPTIBILITY MAP SPECIFICATIONS

### **Digital compilation**

> The susceptibility values were calculated by combining numerical
> values from ARC/INFO grids for geologic units, slope, and aspect. The
> resulting 10 m grid files were assembled on 1:100,000-scale base maps
> which were derived from U.S. Geological Survey Digital Line Graph
> data. About 20% of the mapped area was covered by 30 m grids, which
> were resampled to produce 10 m grid files (for information regarding
> the specific areas covered by resampled grids, see the open-file
> report text). The digital files and the plot files are arranged on 30'
> X 60' quadrangles. The San Diego 30' X 60' quadrangle includes the
> western part of the El Cajon 30' X 60' quadrangle.

### **Spatial resolution**

> Use of this digital soil-slip susceptibility map database should not
> violate the spatial resolution of the data. Although the digital form
> of the data removes the constraint imposed by the scale of a paper
> map, the detail and accuracy inherent in map scale are also present in
> the digital data. Although the map plot files are released at
> 1:100,000-scale, the elevation and the geologic data were derived from
> 1:24,000-scale data, so plotting the data at this scale is
> permissible. However, the fact that this database was compiled from
> 1:24,000-scale Digital Elevation Models means that higher resolution
> information is not generally present in the dataset. Plotting at
> scales larger than 1:24,000 will not yield greater *real* detail,
> although it will reveal irregularities above the intended resolution
> of the database.

### **Map accuracy standards**

> The digital elevation data meet U.S. Geologic National Digital
> Elevation Model standards and the geologic data meet national geologic
> map standards.

### **Database specifics**

**[General]{.underline}**\--The map database consists of ARC/INFO format
grids, which are stored in universal transverse mercator (UTM)
projection, zone 11 (Table 1), and a series of data tables.

  ---------------- ------------------------------------------------------
  Table 1 \-\--    Map Projection

  Projection       UTM

  Datum            NAD27

  Zunits           No

  Units            Meters

  Spheroid         Clark 1866

  X shift          0.000000000

  Y shift          0.000000000
  ---------------- ------------------------------------------------------

The database is composed of ARC/INFO grids, which are raster data files
composed of cells. Definitions of the database items are explained in
Table 2.

Table 2 -- Item Definition Terms

ITEM NAME Name of the database field

WIDTH Maximum number of digits or characters stored

OUTPUT Output width

TYPE B-binary integer, F-binary floating point number, I-ASCII integer,
C-ASCII character string

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

Table 3 -- Items, Value Attribute Table (\*\_sus.vat)

ITEM NAME WIDTH OUTPUT TYPE N. DEC.

VALUE 4 10 B - Default item for cell values

COUNT 4 10 B - Number of cells with specific value

SUSCODE 8 8 N 3 Item containing susceptibility

values

The grid cell values range from 0 to 5000, though not all of the grids
use the full range of values. A cell value of zero indicates the cell
does not meet the criteria needed to fall into the low, moderate, or
high susceptibility categories. Cell values greater than zero are
divided into 3 classes representing low, moderate, and high
susceptibility. Areas of low susceptibility include values ranging from
6 to 999, areas of moderate susceptibility include values ranging from
1000 to 3250, and areas of high susceptibility include values ranging
from 3251 to 5000.

# REFERENCES

Environmental Systems Research Institute, Inc, 1991, ARC/INFO command
references 6.0: Proprietary software manual.

Appendix I (metadata text)

Identification_Information:

Citation:

Citation_Information:

Originator: Douglas M. Morton

Originator: Rachel M.H. Alvarez

Originator: Russell H. Campbell

Publication_Date: 200301

Title: Preliminary Soil-Slip Susceptibility Maps, Southwestern
California

Edition: Version 1.0

Geospatial_Data_Presentation_Form: raster digital data

Series_Information:

Series_Name: U.S. Geological Survey Open-File Report

Issue_Identification: USGS OF 03-17

Publication_Information:

Publication_Place: Menlo Park, California

Publisher: U.S. Geological Survey

Online_Linkage: http://geopubs.wr.usgs.gov/open-file/of03-17

Description:

Abstract:

This data set maps the soil-slip susceptibility for several areas in
southwestern California. Created using Environmental Systems Research
Institute\'s ARC/INFO software, the data base consists of raster maps
containing grid cells coded with soil-slip susceptibility values. In
addition, the data set includes the following graphic and text products:
(1) postscript graphic plot files containing the soil-slip
susceptibility map, topography, cultural data, and a key of the colored
map units, and (2) PDF and text files of the Readme (including the
metadata file as an appendix) and accompanying text, and a PDF file of
the plot files.

Intense winter rains commonly generated debris flows in upland areas of
southwestern California. These debris flows initiate as small landslides
referred to as soil slips. Most of the soil slips mobilize into debris
flows that travel down slope at varying speeds and distances. The debris
flows can be a serious hazard to people and structures in their paths.
The soil-slip susceptibility maps identify those natural slopes most
likely to be the sites of soil slips during periods of intense winter
rainfall. The maps were largely derived by extrapolation of debris-flow
inventory data collected from selected areas of southwestern California.
Based on spatial analyses of soil slips, three factors in addition to
rainfall, were found to be most important in the origin of soil slips.
These factors are geology, slope, and aspect. Geology, by far the most
important factor, was derived from existing geologic maps. Slope and
aspect data were obtained from 10-meter digital elevation models (DEM).
Soil-slip susceptibility maps at a scale of 1:24,000 were derived from
combining numerical values for geology, slope, and aspect on a 10-meter
cell size for 128 7.5' quadrangles and assembled on 1:100,000-scale
topographic maps. The resultant maps of relative soil-slip
susceptibility represent the best estimate generated from available
debris-flow inventory maps and DEM data.

Purpose: These data sets were derived to describe the relative soil-slip
susceptibility for upland areas of southwestern California. Although
released on a 1:100,000-scale topographic base, the data were derived at
a scale of 1:24,000 and as such can be transferred from 1:100,000-scale
to 1:24,000-scale without any loss of accuracy. The maps are not
intended to be used at any scale larger than 1:24,000.

Supplemental_Information: none

Time_Period_of_Content:

Time_Period_Information:

Single_Date/Time:

Calendar_Date: 2003/01

Currentness_Reference: Not for use after June, 2003

Status:

Progress: Complete

Maintenance_and_Update_Frequency: None planned

Spatial_Domain:

Bounding_Coordinates:

West_Bounding_Coordinate: -120.00446939

East_Bounding_Coordinate: -116.8742505

North_Bounding_Coordinate: 34.52044023

South_Bounding_Coordinate: 32.49939779

Keywords:

Theme:

Theme_Keyword_Thesaurus: none

Theme_Keyword: Soil slips

Theme_Keyword: Debris flows

Place:

Place_Keyword_Thesaurus: none

Place_Keyword: California

Place_Keyword: Southwestern California

Place_Keyword: Los Angeles County

Place_Keyword: Orange County

Place_Keyword: Riverside County

Place_Keyword: San Bernardino County

Place_Keyword: San Diego County

Place_Keyword: Santa Barbara County

Place_Keyword: Ventura County

Access_Constraints: none

Use_Constraints: This data base is not to be used at a scale larger than
1:24,000.

Point_of_Contact:

Contact_Information:

Contact_Person_Primary:

Contact_Person: Douglas M. Morton

Contact_Organization: U.S. Geological Survey, Western Region, Earth
Surface Processes Team

Contact_Position: Project geologist

Contact_Address:

Address_Type: mailing address

Address: U.S. Geological Survey

Address: Department of Earth Sciences

Address: University of California, Riverside

City: Riverside

State_or_Province: California

Postal_Code: 92521

Country: United States of America

Contact_Voice_Telephone: (909) 276-6397

Contact_Facsimile_Telephone: (909) 276-6295

Contact_Electronic_Mail_Address: scamp@usgs.gov

Data_Set_Credit: Geologic mapping and digital preparation of this report
were sponsored jointly by (1) the National Cooperative Geologic Mapping
Program of the U.S. Geological Survey, (2) the California Geological
Survey, and (3) the Southern California Areal Mapping Project (SCAMP).
The California Geological Survey graciously provided geologic map data
and critical input.

Native_Data_Set_Environment:

Windows_NT, 5.0, Intel

ARC/INFO version 8.1

Data_Quality_Information:

Attribute_Accuracy:

Attribute_Accuracy_Report: The map meets national geologic map
standards. The digital elevation data meet U.S. Geological National
Digital Elevation Model standards.

Logical_Consistency_Report: Not applicable for raster data.

Completeness_Report: The map reflects the most accurate geologic map
data and DEM data currently available to the U.S. Geological Survey.

Positional_Accuracy:

Horizontal_Positional_Accuracy:

Horizontal_Positional_Accuracy_Report: For accuracy information for DEM
data refer to the U.S. Geological Survey Digital Elevation Models, Data
User\'s Guide 5. Complete reference is in the explanatory text document.

Lineage:

Process_Step:

Process_Description: Process included mapping debris flows from several
generations of aerial photographs in selected areas of southwestern
California. Debris flows were transferred by inspection to 7.5'
topographic quadrangle maps to produce debris flow inventory maps.
Debris flow inventory maps were digitized in a GIS system (Arc/Info).
Geologic data were obtained from digital geologic data bases from
various sources. Digital elevation data were obtained from U.S.
Geological Survey digital elevation models (DEM). Susceptibility values
were the product of numerical values assigned to geologic map units,
slope, and aspect.

Process_Date: 200209-200301

Process_Step:

Process_Description:

First draft of metadata created by Rachel Alvarez using

FGDCMETA.AML ver. 1.2 05/14/98 on ARC/INFO data set

Process_Date: 20030108

Process_Step:

Process_Description: Digital database review by Scott Graham.

Process_Date: 20030113

Spatial_Data_Organization_Information:

Direct_Spatial_Reference_Method: Raster

Raster_Object_Information:

Raster_Object_Type: Grid Cell

Row_Count: 22569

Column_Count: 29031

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:

Planar:

Grid_Coordinate_System:

Grid_Coordinate_System_Name: Universal Transverse Mercator

Universal_Transverse_Mercator:

UTM_Zone_Number: 11

Transverse_Mercator:

Scale_Factor_at_Central_Meridian: 1

Longitude_of_Central_Meridian: -118 26 15

Latitude_of_Projection_Origin: 32 30

False_Easting: 0

False_Northing: 0

Planar_Coordinate_Information:

Planar_Coordinate_Encoding_Method: coordinate pair

Coordinate_Representation:

Abscissa_Resolution: 10.0

Ordinate_Resolution: 10.0

Planar_Distance_Units: Meters

Geodetic_Model:

Horizontal_Datum_Name: North American Datum of 1927

Ellipsoid_Name: Clarke 1866

Semi-major_Axis: 6378206.4

Denominator_of_Flattening_Ratio: 294.98

Entity_and_Attribute_Information:

Overview_Description:

Entity_and_Attribute_Overview:

Version 1.0 of the Preliminary Soil-Slip Susceptibility Maps,
Southwestern California comprises seven ARC/INFO grids, la_sus, lb_sus,
ocs_sus, sbern_sus, sd_sus, sa_sus, sbarb_sus, which contain soil-slip
susceptibility values. The item names and definitions are the same for
each raster data set and are as follows:

\*\_sus.vat

COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME

1 VALUE 4 10 B -

5 COUNT 4 10 B -

9 SUSCODE 8 8 N 3

\*\_sus.sta

COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME

1 MIN 8 15 F 3

9 MAX 8 15 F 3

17 MEAN 8 15 F 3

25 STDV 8 15 F 3

The item suscode contains the susceptibility values.

Entity_and_Attribute_Detail_Citation: none

Detailed_Description:

Entity_Type:

Entity_Type_Label: \*.vat

Entity_Type_Definition: Susceptibility values identified in each of the
seven mapped areas (the Santa Barbara 100K sheet, the Los Angeles 100K
sheet, the south half of the San Bernardino 100K sheet, the Long Beach
100K sheet, the Santa Ana 100K sheet, the Oceanside 100K sheet, and the
San Diego and western El Cajon 100K sheets)

Attribute:

Attribute_Label: suscode

Attribute_Definition: number corresponding to a susceptibility value =
not included in low, moderate or high

Attribute_Domain_Values:

Enumerated_Domain:

Enumerated_Domain_Value: 0

Enumerated_Domain_Value_Definition: A value of 0 indicates the cell does
not meet the criteria needed to fall into the low, moderate or high
susceptibility categories.

Susceptibility values identified in each of the seven mapped areas (the
Santa Barbara 100K sheet, the Los Angeles 100K sheet, the south half of
the San Bernardino 100K sheet, the Long Beach 100K sheet, the Santa Ana
100K sheet, the Oceanside 100K sheet, and the San Diego and western El
Cajon 100K sheets).

Attribute:

Attribute_Label: suscode

Attribute_Definition: number corresponding to a susceptibility value =
low

Attribute_Domain_Values:

Range_Domain:

Range_Domain_Minimum: 6

Range_Domain_Maximum: 999

Attribute:

Attribute_Label: suscode

Attribute_Definition: number corresponding to a susceptibility value =
moderate

Attribute_Domain_Values:

Range_Domain:

Range_Domain_Minimum: 1000

Range_Domain_Maximum: 3250

Attribute:

Attribute_Label: suscode

Attribute_Definition: number corresponding to a susceptibility value =
high

Attribute_Domain_Values:

Range_Domain:

Range_Domain_Minimum: 3251

Range_Domain_Maximum: 5000

Distribution_Information:

Distributor:

Contact_Information:

Contact_Organization_Primary:

Contact_Organization: U.S. Geological Survey Information Services

Contact_Address:

Address_Type: mailing address

Address: Box 25286 Denver Federal Center

City: Denver

State_or_Province: Colorado

Postal_Code: 80225

Country: USA

Contact_Voice_Telephone: (303) 202-4700

Contact_Facsimile_Telephone: (303) 202-4693

Distribution_Liability:

The U.S. Geological Survey (USGS) provides these geographic data \"as
is\". The USGS makes no guarantee or warranty concerning the accuracy of
information contained in the geographic data. The USGS further makes no
warranties, either expressed or implied as to any other matter
whatsoever, including, without limitation, the condition of the product,
or its fitness for use lies entirely with the user. Although these data
have been processed successfully on computers at the USGS, no warranty,
expressed or implied, is made by the USGS regarding the use of these
data on any other system, nor does the fact of distribution constitute
or imply any such warranty.

In no event shall the USGS have any liability whatsoever for payment of
any consequential, incidental, indirect, special, or tort damages of any
kind, including, but not limited to, any loss of profits arising out of
use of or reliance on the geographic data or arising out of the
delivery, installation, operation, or support by USGS.

These digital map databases, 1:100,000 scale, and any derivative maps
thereof, is not meant to be used or displayed at any scale larger than
1:24,000 (e.g., 1:12,000).

Metadata_Reference_Information:

Metadata_Date: 20030108

Metadata_Review_Date: 20030113

Metadata_Contact:

Contact_Information:

Contact_Organization_Primary:

Contact_Organization: U.S. Geological Survey

Contact_Person: Rachel M.H. Alvarez

Contact_Position: Geologist

Contact_Address:

Address_Type: mailing address

Address: U.S. Geological Survey

Address: Department of Earth Sciences

Address: University of California, Riverside

City: Riverside

State_or_Province: California

Postal_Code: 92521

Country: USA

Contact_Voice_Telephone: (909) 276-6397

Contact_Facsimile_Telephone: (909) 276-6295

Contact_Electronic_Mail_Address: rhauser@usgs.gov

Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial
Metadata

Metadata_Standard_Version: FGDC-STD-001-1998

Metadata_Access_Constraints: none

Metadata_Use_Constraints: none