"FRESNO, Calif. — The government has been collecting dirt — lots of it.

Clumps came from the Texas Panhandle, a shady grove in West Virginia, a picked-over corn field in Kansas and thousands of other places in the lower 48 states.

A small army of researchers and university students lugging pick axes and shovels scattered across the country for three years to scoop samples into plastic bags from nearly 5,000 places. They marked the GPS coordinates, took photos and labeled each bag before mailing them back to the government's laboratory in Denver."

Scott Smith reports for the Associated Press March 29, 2014. [2]