With the number of Computer Science (CS) jobs on the rise, there is a greater need for Computer Science graduates than ever. At the same time, most CS departments across the country are only seeing 25 to 30 percent of female students in their classes, meaning that we are failing to draw interest from a large portion of the population. In this work, we explore the gender gap in CS at a large public research university, using three data sets that span thousands of students across 5 and a half academic years. By combining these data sets, we can explore many issues such as retention as students progress through the CS major. For example, we find that a large percentage of women taking the Introductory CS1 course for majors do not intend to major in CS, which contributes to a large increase in the gender gap immediately after CS1. This finding implies that a large part of the retention task is attracting these women to further explore the major. We report findings in three areas of research in the context of the CS department at our university: the CS environment, the computing background of our students, and the students' grades. These findings may also be applicable to computing programs at other large public research universities.