While studying the extension of the region, geologist John West of ASU was surprised to find that something unusual existed beneath this area's surface. West and colleagues found that portions of the lithosphere--the crust and uppermost mantle of the Earth--had sunk into the more fluid upper mantle beneath the Great Basin and formed a large cylindrical blob of cold material far below the surface of central Nevada.
http://www.sciencedaily.com/releases/2009/05/090526171813.htm