I was surprised to learn that the median senior engineer earns only $36K more than the median junior engineer (base salary only). The gap does get wider on the right tail of the distribution: The 90th-percentile senior makes $47K more than the 90th-percentile junior.
One possible explanation is that our data is dominated by startups, which lean toward equity-heavy compensation. The range in equity is so big we had to plot it on a logarithmic scale.