Mayor Libby Schaaf was spelling out the “huge anxiety around gentrification” in Oakland during last week’s event on income inequality sponsored by the Public Policy Institute of California.

“Normally you would celebrate when an employer like Uber moves its headquarters into your city because it’s going to create 2,000 to 3,000 jobs,” Schaaf explained. “And yet there’s a huge fear that those types of jobs are actually going to create more poverty and drive poor and even working-class families out of a city they’ve called home for generations.”

Schaaf noted that three of the five most expensive cities to rent an apartment in the United States are in the Bay Area: San Francisco, San Jose and Oakland.

“This is how income inequality is really manifesting itself in Oakland ... an absolute fear and anger around gentrification,” Schaaf said at the panel I moderated in Sacramento on Monday.

I turned to panelist Ashley Swearengin, mayor of Fresno, and asked whether gentrification was a stress point in her city. Her one-word answer: no.

“What I was actually sitting here thinking is: Could we somehow merge Oakland and Fresno?” Swearengin said, drawing laughter from the audience.

The two mayors’ contrasting portrayals of a common challenge — serious gaps in wealth and opportunity — underscored the findings of a new PPIC report, “Income Inequality and the Safety Net in California.”

On a statewide level, the trend is readily apparent. “Since 1997, the per capita gross domestic product has increased by more than 30 percent in California,” the PPIC report noted. “Over this same period, top incomes have grown at more than double the rate of low and middle incomes. This seems contrary to the idea that ‘a rising tide lifts all boats.’”

The Fresno-Oakland experiences make plain that there is no one-size-fits-all solution to addressing the disparities in wealth — and more important for the long-term preservation of the California Dream: opportunity — in a state this large and diverse. One city suffers the effects of overbuilding and a sparse employment base, while the other’s housing prices and rents are feeling the pressure of a region’s hyperprosperity.

Swearengin attributed Fresno’s predicament to the years “we blew out our borders” to stretch into erstwhile farmland that was cheap, flat and easy to convert to residential.

“As our community has expanded dramatically over the years, we have left behind neighborhoods with no underlying economy to really support and maintain those neighborhoods,” Swearengin said. “So we’ve ended up with this very stark line between neighborhoods with discretionary income and a very high concentration of neighborhoods south of that line.”

Amplifying a theme in the PPIC report, Swearengin suggested the state needed to come up with strategies to help buffer the distribution of jobs and investment between the coastal and central areas of the state.

“Bay Area incomes at the bottom, middle and top are roughly twice that of incomes in the Central Valley and Sierra region,” the report said. The latter two areas also had a more pronounced wealth-poverty divide.

There were two clear takeaways from that session. One was how many points the two mayors, Schaaf a Democrat and Swearengin a Republican, had in common: Each expressed an unalloyed commitment to addressing both poverty and economic development in their communities. Such is the nature of big-city mayors, who tend to be held accountable by results and can ill afford the ideological rigidity and partisan sideshows that too often preoccupy our elected representatives in Washington or even Sacramento.

Another bottom line was apparent in both the report and the panel discussion: Education is essential to keeping this disturbing trend from metastasizing into a permanent affliction on the state. Last year the PPIC issued a report that projected California would be short 1.1 million college-educated workers by 2020.

Schaaf’s “Oakland Promise” program attempts to raise funds for efforts to triple the number of college graduates from the city; Swearengin cited Fresno’s development of an entrepreneurship curriculum in fifth and sixth grades — and a high school dedicated to entrepreneurship — to uplift the skills and expectations of the city’s youth.

Neither mayor had a firm answer for one of the PPIC report’s daunting concluding questions: “What level of income inequality is acceptable or economically optimal?” After all, a certain level of inequality is inevitable, and in many ways beneficial to a society: It creates an incentive for hard work and ambition.

But when someone born in the bottom fifth of economic strata has just an 8 percent chance of reaching the top fifth in his or her lifetime — a national statistic invoked by Swearengin, a Republican — something is terribly amiss. The existential threat to the California Dream is real, it is ominous and, as the new report shows, it is growing.

John Diaz is The San Francisco Chronicle’s editorial page editor. Email: jdiaz@sfchronicle.com Twitter: JohnDiazChron

A state of great prosperity and deep poverty

Among the findings in a new report by the Public Policy Institute of California:

Going up,

going down

39.7% Increase in incomes statewide in the 90th percentile between 1980 and 2014.

5% Increase in incomes statewide in the 50th percentile between 1980 and 2014

18.6% Decrease in incomes statewide in the 10th percentile betwe e n 1980 and 2014

Variations among regions

$252,000 Income threshold for 90th percentile in Bay Area, 2014

$184,000 Income threshold for 90th percentile in Los Angeles County, 2014

$147,000 Income threshold for 90th percentile in Central Valley and Sierra, 2014

Who’s

falling behind?

Single-parent families are 2.2 percent more likely to fall in the bottom quintile of incomes statewide.

Families with workers who have less than a high school diploma are 2.6 times more likely to be in the bottom quintile of incomes statewide.