STEPTOE, Wash. — David Benscoter honed his craft as an investigator for the F.B.I. and the United States Treasury, cornering corrupt politicians and tax evaders. The lost apple trees that he hunts down now are really not so different. People and things, he said, tend to hide in plain sight if you know how and where to look.

“It’s like a crime scene,” Mr. Benscoter, 62, said as he hiked down a slope toward a long-abandoned apple orchard planted in the late 1800s. “You have to establish that the trees existed, and hope that there’s a paper trail to follow.”

About two-thirds of the $4 billion apple industry is now concentrated in Washington State — and 15 varieties, led by the Red Delicious, account for about 90 percent of the market. But the past looked, and tasted, much different: An estimated 17,000 varieties were grown in North America over the centuries, and about 13,000 are lost.

From New England through the Midwest and the South to Colorado and Washington, where small family farms were long anchored by an orchard, most apple trees died along with the farms around them as industrial-scale agriculture conquered American life a century ago.