The Great Basin and its mountain ranges formed millions of years ago when geological forces pulled on the Earth's crust. As that happened, volcanoes erupted across the Basin, which extends from eastern California to central Utah.

G. Lang Farmer, co-author of a new report on plate tectonics and the Sierra Nevada Mountains, said he is excited about an Internet site that allows the public to locate these ancient volcanoes. He is a member of the steering committee for the effort.

The project is the Western North American Volcanic and Intrusive Rock Database. Going by the acronym NAVDAT, its Web home page is navdat.geo.ku.edu. A search on the site turns up a profusion of extinct volcanoes throughout the western part of the Beehive State, with the biggest concentration in southwestern Utah.

Although the site's data are largely technical, the map shows where volcanic activity took place.

The ancient craters, lava flows, domes and other evidence of volcanism are arranged almost in the shape of a dipper, with the bowl to the south. NAVDAT found 299 records pertaining to the Utah eruptions.

Anyone interested in the subject can "look for themselves," said Farmer, and see where volcanic activity took place in this state over the past 70 millions. Utahns can "find out what was going on in their own back yard."