VISALIA, Calif.—California's agricultural Central Valley has thrived for decades on Americans' seemingly endless appetites. Now, with U.S. market growth slowing, farmers are going after a different group of consumers: middle-class Chinese attracted to Western fare like milk and almonds.

Consider Dave Bush, operating chief of California Dairies Inc. Mr. Bush recently discovered that the dairy cooperative, the nation's second-largest, wasn't exporting very much to China, whose population is now the world's...