  A young, nearby compact aggregate of X-ray emitting pre-main sequence stars
was recently discovered in the vicinity of eta Cha (B8V). In this paper, we
further investigate this cluster: its membership, its environs and origins.
ROSAT HRI X-ray data for the cluster's T Tauri stars show high levels of
magnetic activity and variability. The cluster has an anomalous X-ray
luminosity function compared to other young clusters, deficient in stars with
low, but detectable X-ray luminosities. This suggests that many low-mass
members have escaped the surveyed core region. Photographic photometry from the
USNO-A2.0 catalog indicates that additional, X-ray-quiet members exist in the
cluster core region. The components of the eclipsing binary RS Cha, previously
modeled in the literature as post-MS with discordant ages, are shown to be
consistent with being coeval pre-MS stars. We compute the Galactic motion of
the cluster from Hipparcos data, and compare it to other young stars and
associations in the fourth Galactic quadrant. The kinematic study shows that
the eta Cha cluster, the TW Hya association, and a new group near epsilon Cha,
probably originated near the giant molecular cloud complex that formed the two
oldest subgroups of the Sco-Cen OB association roughly 10-15 Myr ago. Their
dispersal is consistent with the velocity dispersions seen in giant molecular
clouds. A large H I filament and dust lane located near eta Cha has been
identified as part of a superbubble formed by Sco-Cen OB winds and supernova
remnants. The passage of the superbubble may have terminated star-formation in
the eta Cha cluster and dispersed its natal molecular gas.
