Hertzsprung–Russell (H-R) diagram for 1633 CDDS stars in stellar associations, clusters, and moving groups (ACMG). The light-blue (lime, fuchsia) curves shows the PARSEC 1.2S isochrone for [Fe/H] = 0 and an age of 3 Myr (20, 150 Myr), displaced by −500 K (0 K, +750 K) for clarity. The lower bound of the two curves for T_eff ≳ 15,000 K (light blue) and T_eff ≲ 15,000 K (fuchsia) marks the approximate zero-age main sequence (ZAMS); all CDDS stars lie above this locus. For cooler stars, the 3 Myr isochrone sets a strong upper limit to the set of young stars contracting to the main sequence. Some cluster stars lie at the main-sequence turnoff for ages 20–150 Myr.