In 2001, the US Fish and Wildlife Service contracted with the Department of Geography and Planning and the Geographical Information Center at California State University, Chico to develop a set of historic natural vegetation maps for the Great Central Valley of California.

Four period maps (pre-1900, 1945, 1960, and 1995) were produced that identify major changes that have occurred in the Great Central Valley due in part to hydrologic alterations associated with the Central Valley Project (1945) and the California State Water Project (1973). The maps were scanned and digitized into a geographical information system ("GIS") in an effort to quantify vegetation changes in the valley over the past 100 years.

Developing the map set and GIS consisted of researching libraries for archival information, developing GIS tools for data input, and displaying and analyzing information from a variety of sources. The best information available on the Great Central Valley was gathered in order to create a bank of accessible information from which future and more detailed analysis can be undertaken.