U.S.G.S Topographic Maps

California (DRG) GEOTIFF Images

Until recently, U.S.G.S. DRG files were  freely available on the Internet.  These files are the digital equivalents of paper U.S.G.S. 7.5' topographic maps.  However, private companies are now charging for the digital map files that were created by the U.S.G.S.  Fortunately, the state of California has an agreement with the Federal government that makes the files available free of charge (California only) through a server located at UC-Davis.  For reasons that are not clear the front-end that allows you to readily locate the map you need was never completed.  The maps simply exist in folders arranged by latitude and longitude with no index.  The Geological Sciences Department at Cal Poly is attempting to create an index for these maps (see instructions below).  At present we have created an index for eleven counties in southern/central California, but plan to expand that over the next year (2002).

Counties currently completed are:

• Los Angeles

• Orange

• Riverside

• San Bernardino

• Imperial

• San Diego

• Santa Barbara

• San Luis Obispo

• Inyo

• Kern

• Mono

To obtain the map you need follow these steps

1. If you don't know the quadrangle maps you need click on this link to MapMart.  Make sure you are in the U.S.G.S DRG section. Under Choose a Size make sure 1:24,000 is selected and click on the Begin Search button to the right.  You will be presented with a zoomable map of the United States.  Click on California and proceed to Zoom In until you find the names of the quadrangles you want.  If those quads are in one of the eleven counties listed above, proceed to step two.  If not, you are on your own for now.

2. Click on this link to the Cal Poly Topomap Database.  Using your browsers Find command, enter the name of the quad(s) you are seeking.  You will see a seven character alphanumeric number next to the quad name.  Write this number down and click the back button on your browser.  You are now ready to go to step three.

3. Click on this link to go to the UC-Davis Map server.  Scroll down to the bottom of the page and you will see a list of folders.  Select the 7.5_minute_series_albers_nad27_untrimmed folder.  A new list of folders will apear, The numbering should correspond to the first five digits of your quad sheet index number.  Click on the pertinent folder and you will see a long list of files. Locate your quad on the index map or from the list; double click on the file (.tif) or index map to download the quadrangle. Note: there is also an accompanying .tfw file. That file is used to auto-register your quad with GIS software. However, since the rest of the world does not use the Albers system you will find your quad has been registered somewhere in the mid-Pacific by most GIS programs!. Use the registration marks and do it the old-fashioned way!