When Lola Arce de Quintela first moved to Oakton 20 years ago, she noticed something about the way men and women arranged their professional careers around their family lives in Northern Virginia. Men took high-powered jobs with large paychecks, while women often dropped out of the workforce to take care of growing families. If women had full-time jobs, she says, they would often select positions that were not as demanding so they could focus their time and attention on their children while husbands and fathers pulled in six-figure salaries.

"The other women who live on my block are teachers," said de Quintela, a freelance translator. "Their husbands are attorneys or they work for the World Bank."

On a national basis, women make 77 cents for every dollar men make. But here in Northern Virginia the disparities are greater, especially in wealthier areas. Nowhere is this trend the highest than 22124, the suburbs of Oakton, where the average median income for full-time female workers is $77,000. The men in that ZIP code pull in almost $130,000. That means women who live in Oakton earn 60 percent of what men earn.

"It's very difficult to have a family and raise kids when you have two people with high-powered careers that demand a lot of time and attention," said de Quintela. "So a lot of women tend to find work that's more flexible and not as demanding, which means they earn less money. It's a trade off."

CENUS RECORDS show disparities are greatest where people earn the most money. In the Fairfax Station ZIP code 22039, for example, the average annual male median salary is $134,000. That's one of the highest in Northern Virginia. By contrast, women in this area earn $86,000 a year. That's still a high salary for the region, women who live in Fairfax Station earn 64 cents for every $1 the men who live there make. Demographers say some of this may be explained by a concept they call "labor force attachment," which essentially means that women are less attached to the labor force than men.

"Given the traditionally understandings about who cares for children or aging parents, what we often see is that women take on those roles," said Annie Rorem, policy associate in the demographics research group at Weldon Cooper Center for Public Service at the University of Virginia. "We often see differences in female and male earnings often that are related to, although I would not necessarily say caused by, family structure."

This trend is less evident in ZIP codes where salaries are lower, and the roles are even reversed in some of areas with the lowest salaries. In Bailey's Crossroads, for example, women earn $59,000. But men earn $46,000, the lowest salary of any Fairfax County ZIP code. That means men earn about 22 percent less than women here, a phenomenon that indicates workers here are attached to the labor force in a way that's different from people at the top of the earnings scale.

"What we are probably seeing in Bailey's Crossroads is women who are nannies of families that make a lot of money," said Veronique de Rugy, a senior research fellow at the Mercatus Center at George Mason University. "They make a lot more money than their male counterparts who are working in construction or putting up drywall."

ACADEMICS WHO look at these numbers say the imbalance of salaries between men and women can be explained by looking at how the genders participate in the labor force differently. A recent study by the George Mason School for Regional Analysis concluded that Arlington County has the highest labor force participation rate for women in the region while the District of Columbia has the lowest. Meanwhile, suburban areas of Fairfax County have much lower female participation rates than urban areas such as Arlington or Alexandria.

"If you're looking at why men are earning more, it's because in those cases women who might have a higher earning potential are not in the labor force, they are staying home to raise a family," said David Versel, senior research associate at the Center for Regional Analysis. "That's obviously less true than it was a generation or two ago, but that's the easiest way of looking at this."

Although the disparity between salaries earned by men and women are glaring, researchers who look at the data warn not to jump to conclusions about gender inequality. These numbers show that men and women who live in the same ZIP codes earn different salaries, it does not say that they receive different salaries for doing the same work. So they probably say more about how women and men approach the labor force differently than how employers choose to compensate their employees.

"This doesn't necessarily mean that we are talking about any active gender inequality in the sense of discrimination or men and women being paid different amounts for the exact same labor," said Rorem. "One thing that's important to keep in mind when you are looking at all full-time year-round workers is that one thing you don't pick up is experience between workers."