Should-Read: Bridget Ansel: Climbing the career ladder, switching jobs, and the gender wage gap in the United States: "For workers with a college education, gender-based gaps in pay are primarily caused by disparities that emerge within a single workplace... http://equitablegrowth.org/equitablog/climbing-the-career-ladder-switching-jobs-and-the-gender-wage-gap-in-the-united-states/
...men get raises and promotions at a significantly higher rate than their female colleagues do.... Time or effort... put into paid employment... working long hours—even without a proportional rise in actual output—can result in disproportionate economic rewards. Harvard University economist Claudia Goldin calls this “the last chapter” in attaining gender equality.... A difference in men and women’s tendency to negotiate.... [But] while women may be more reluctant to negotiate, that’s partly due to the fact that it doesn’t go as well for them when they do.
Barth, Kerr, and Olivetti find there is a smaller widening in pay over their lifetimes for men and women who are not college-educated—and this is not primarily driven by the disparities that emerge within a single workplace. Instead, the widening pay gap for non-college workers largely derives from differences between men and women in where they work and their “job mobility,” or how often workers change jobs, and the kinds of pay increases they get when they do..."