As emphasized in the 2021 Snowmass report (Bechtol et al. 2022; Drlica-Wagner et al. 2022; Chou et al. 2022) sampling the halo mass function at the boundary between galactic and sub-galactic scales (k ∼ 100) will allow simultaneous tests of the astrophysical processes and dark matter physics that govern the faint end of galaxy formation. Dwarf galaxies are extremely dark-matter-dominated systems, and Spec-S5 provides the capability to map the dark matter halo density profiles of the higher-mass dwarfs, as well as determine the kinematics of lower-mass dwarf galaxies out to their tidal radii (including new dwarf galaxies discovered from the Rubin/LSST imaging survey).