[Mg/Fe] vs. [Fe/H] for the subset of DR4 used in this paper. The gray lines denote the different metallicity and [Mg/Fe] bins used in later sections. We separate populations likely belonging to the thin and thick disks using the [Mg/Fe] ratio, with higher [Mg/Fe] stars likely belonging to the thick disk denoted in red and lower [Mg/Fe] stars likely belonging to the thin disk in blue.