The first fully digitized geological map of Alaska, the product of two decades of work, was released Tuesday by the U.S. Geological Survey.

To create the map and its voluminous supporting material, "I basically used everything I could possibly find," said USGS research geologist and lead author Frederic Wilson. That included everything from field notes made by geologists in the 1950s and earlier -- even some information more than a century old -- to the most modern information available from sources like Google Earth and satellite imagery, he said.

The map ultimately used more than 750 sources to detail the state's surface geology, and is accompanied by a 204-page document and supporting databases for explanatory details and color codes for different types of rock.

The mapping project, funded in part by the National Park Service, was started in the mid-1990s, Wilson said. There were two triggers -- a request from the Alaska Division of Oil and Gas, which wanted more geological information about Interior Alaska, and a national mapping initiative that had the goal of creating digitized maps for all 50 states, he said.

Wilson was put in charge of the Alaska and Hawaii portions of the USGS Surveys and Analysis program, making him one of the four regional leaders of the national program.

The Alaska product displays the digitized images at a scale of about 25 miles per inch on a full-size printed map, compared to a scale of 40 miles per inch for many older geologic maps, Wilson said, allowing for a greater level of detail.

Gathering the information that went into the map required consultation with older geologists who worked in Alaska decades ago; some were retired USGS scientists who have died in the years since the project got underway in 1996.

The information-gathering mission also required some site visits to fill in gaps. In the Dillingham area, for example, older maps created with aerial data proved to be wrong, he said.

"Sometimes you just had to go back out there," Wilson said.

At some sites, changes since the mid-20th century were detected. Wilson's team had some detailed maps of Lake Clark National Park glaciers that were made in the 1950s, for example; the new digitized map incorporates images gathered by satellite in 2006 and they are not the same, he said.

"We could see that there's a 13 percent loss in the area of the glaciers," he said.

Some gaps still exist but that information can be added in the future as it is acquired, Wilson said.

The project has some important economic benefits, Sen. Lisa Murkowski said in a statement issued by the USGS.

"A better understanding of Alaska's geology is vital to our state's future. This new map makes a real contribution to our state, from the scientific work it embodies to the responsible resource production it may facilitate," she said in the statement.

Mark Myers, commissioner of the Alaska Department of Natural Resources, said the digitized map will have a variety of uses.

"This work is an important synthesis that will both increase public access to critical information and enhance the fundamental understanding of Alaska's history, natural resources and environment," Myers said in the USGS statement, adding that it could aid in such fields as disaster preparedness, resource development, land use planning and education.

The map and its associated products are free to the public, Wilson said, though a specialized type of software is needed to create derivative versions with the supporting databases.

For Wilson, who did his early field work in the Ahklun Mountains of Southwest Alaska and the Tanana Uplands of eastern Alaska, the new digitized map gives him a more complete look at the state, and is much more than the typical work project.

"It's been my passion for years," he said.