During the Great Depression, some 1.3 million Americans—epitomized by the Joad family in John Steinbeck's "The Grapes of Wrath"—flocked to California from the heartland. To keep out the so-called Okies, the state enacted a law barring indigent migrants (the law was later declared unconstitutional). Los Angeles even set up a border patrol on the city limits. Soon the state may need to build a fence to keep latter-day Joads from leaving.

Over the past two decades, a net 3.4 million people have moved out of California for other states. But contrary to conservative lore, there has been no millionaires' march to Texas or other states with no income tax. In fact, since 2005 California has experienced a net in-migration of households earning more than $200,000, according to the U.S. Census's American Community Survey.

As it happens, most of California's outward-bound migrants are low- to middle-income, with relatively little education: those typically employed in agriculture, construction, manufacturing, hospitality and to some extent natural-resource extraction. Their median household income is about $40,000—two-thirds of the statewide median—and about 95% earn less than $80,000. Only one in 10 has a college degree, compared with 30% of California's population. Roughly 40% of the people leaving are Hispanic.

Even while California's Hispanic population has grown by more than 1.5 million since 2005, thanks to high birth rates and foreign immigration, two Hispanics have moved out for every one that has moved in from another state. By contrast, four Hispanics from other states have settled in Texas and Arizona for every three that have left.

It's not unusual for immigrants or their descendants to move in pursuit of a better life. That's the history of America. But it is ironic that many of the intended beneficiaries of California's liberal government are running for the state line—and that progressive policies appear to be what's driving them away.