Data Files
Global Topography and Bathymetry

Converted from the NGDC TerrainBase Global DTM.
National Geophysical Data Center.
Original files: tbase.bin (18 Mb), tbase.hdr (GeoVu format).
Converted netCDF grids, ready for GMT:
5-min grid: tbase5m.grd (35 Mb) removed*
15-min grid: tbase15m.grd (3 Mb), example plot: g.jpeg.
Conversion programs: gv2gmt, grdreformat and grdfilter.
"gv2gmt" converts GeoVu format to GMT short integer format.
"grdreformat" converts GMT short integer to netCDF format.
This is necessary because GMT seems to have some bugs when displaying short integer grids.
"grdsample" was used to sample down to the 15-min grid.

United States Topography

Converted from the NGDC United States 30-Second DTM.
National Geophysical Data Center.
Original files: usa.bin (50 Mb), usa.hdr (GeoVu format).
Converted netCDF grids, ready for GMT:
30-sec grid: usa30.grd (100 Mb) removed*
60-sec grid: usa60.grd (25 Mb) removed*
, example plot: cal.jpeg.
Conversion programs: gv2gmt, grdreformat and grdfilter.
Global topography gridded at 30 seconds is also available from the USGS.

Southern California Topography (121W/115W/32.5N/35.5N)

Derived from USGS 1-degree DEMs.
USGS Eros Data Center.
Converted netCDF grids, ready for GMT:
3-sec grid: 03.grd (98 Mb), example plot: gv.jpeg.
6-sec grid: 06.grd (24 Mb), example plot: gv2.jpeg.
18-sec grid: 18.grd (2 Mb), example plot: scal4.jpeg.
Conversion programs: dem2xyz,
"dem2xzy" converts DEMs to xyz points.
"" is the script used to create the grids.
The more detailed 7.5-minute DEMs for California are available online from the CSUN Geography Department.
Both types are also available for California from the CDMG.

Global Seismicity

CNSS Earthquake Catalog is a world-wide catalog that can be searched and downloaded.
Script to convert CNSS format to a GMT readable format: cnss2xy.
A variety of searchable catalogs are also available from the USGS National Earthquake Information Center.

Southern California Seismicity

A searchable catalog for southern California is available from the
SCEC Data Center.
Be sure to use the "Caltech catread" format to receive the full precision in the locations.
Script to convert SCSN format to a GMT readable format: scsn2xy.

California Faults

The digital version of the Jennings 1994 fault map that is plotted in
cal.jpeg is considered proprietary and thus cannot be redistributed here. The map is controlled by the CDMG which claims the data will someday be released for general use. Currently, to access the files you must write to:

James F. Davis
State Geologist
California Division of Mines and Geology
801 K St. MS 12-30
Sacramento, CA 95814

If you know of any freely available digital fault maps, I would like to know. Please drop me a line at:


Global volcano locations and ages.
Source: the Smithsonian's
Global Volcanism Program
Original file: List of Holocene Volcanoes(this file seems to be currently unavailable)
GMT plot file: gvp.xy
Conversion script: gvp2xy


USGS 1:2M scale Digital Line Graphs are a good source of general geographic data such as coastlines, rivers, roads, etc. The coastlines are better than the GMT hi-res coastline. DLGs for the United States are available online from the:
USGS Eros Data Center.
Here is a Perl program to extract different features from a 1:2M DLG in SDTS format: tvp2xy

Data sets converted from 1:2M DLGs:
Download: ca.xy - California coastline and border
Download: ca_isl.xy - California Islands
Download: ca_roads.xy - California roads

*Due to space constraints, some of the converted files are no longer available for download... sorry. Please obtain the data from the original sources and use the provided conversion programs.