An examination of ~625,000 optical spectra of low-mass stars observed as part of the Sloan Digital Sky Survey (SDSS) provides a broad collection of long-lived objects in the Solar Neighborhood that should include members from all three major components of our Galaxy: the younger thin disk, the older thick disk, and the very old halo. These populations have distinct metallicities and kinematics that differentiate them from one another and should be revealed in large spectroscopic surveys, like SDSS, that provide chemical abundance and radial velocity measurements. One complication is that measuring metallicities of M-dwarfs from mid-resolution (R~2000) spectroscopy alone remains a challenge. To better characterize these low-mass stars, we present a set of 536 improved, empirical K and M dwarf spectral classification templates to more accurately determine spectral subtypes and metallicity using best-fit methods. Aided by these results, we construct a photometric metallicity grid in the Gaia [M_G , G-G_RP] diagram that aims to ultimately provide metallicity estimates for M dwarfs based on Gaia data alone. To help with this, we identify a set of 333 benchmark stars we believe to span a broad range of T_eff and [Fe/H] (~ -3.0 to +1.0) values that will form the basis of future programs to calibrate the grid more precisely. Our preliminary estimates of [Fe/H] however already confirm that the most metal-rich stars are located primarily in the thin disk, and also reveal the known effect of Galactic radial migration. In addition, we uncover significant sub-structure in the metallicity distribution of the most metal-poor stars in velocity space, which shows notable differences between Gaia-Enceladus merger stars and true halo objects. The confirmation of these chemodynamic trends validates the improved templates developed in this work. This methodology opens the door to use the dominant population of local M-Dwarfs to trace chemodynamics in the Solar Neighborhood.

Additionally, we use the best-fit templates to identify chromospherically active stars that show evidence of H-alpha emission. We identify ~49,000 active stars and combine astrometric data from Gaia DR3 with SDSS RVs to calculate their 6-D spatial/velocity distributions. We also introduce the tau_active metric, which describes the local concentration of active stars in 3-D kinematic space. Using this tau_active metric and the HDBSCAN clustering algorithm on our sample of low-mass field stars, we identify 40 active streams that are unidentified in previous studies of substructure in the local Galactic disk. We also examine the absolute Z distributions of the active stars and find a plateau in the vertical distribution of active stars are large distances from the plane of the Galaxy, from which we estimate that ~4% of stars are in close, activity-inducing binaries. Furthermore, this activity study of low-mass field stars also unexpectedly revealed a sample of ~650 stars that are chromospherically active but significantly metal-poor and kinematically old. This is surprising as activity is typically associated with youth and these stars appears to be very old. We hypothesize that these peculiar objects are indeed old, and their activity is likely due to tidal interactions with a nearby companion and confirm that. To test this hypothesis, we present results from a pilot program that used the GHOST spectrograph at Gemini South to search for evidence of a close companion for four SDSS active subdwarfs and find that at least two, but possibly three of the targets are indeed in close binary systems. The catalog of active subdwarf binary candidates from SDSS will be essential tools for calibrating the mass-metallicity-luminosity relationship for low-mass subdwarfs.