  We report the Chandra detection of OVII K\alpha absorption at z=0 in the
direction of the z=0.03 Seyfert 1 galaxy Mkn 279. The high velocity cloud
Complex C lies along this line of sight, with HI 21-cm emission and OVI 1032\AA
absorption both observed at velocities of ~ -150 km/s relative to the local
standard of rest. We present an improved method for placing limits on the
Doppler parameter and column density of a medium when only one unresolved line
can be measured; this method is applied to the OVII absorption seen here,
indicating that the OVII Doppler parameter is inconsistent with that of any
low-velocity (Galactic thick disk) or high-velocity OVI (OVI_HV) component.
Direct association of the OVII with the OVI_HV is further ruled out by the high
temperatures required to produce the observed OVI_HV/OVII ratio and the
significant velocity difference between the OVII and OVI_HV lines. If the OVII
absorption is associated with a very broad, undetected OVI component, then the
absorption must be broadened by primarily nonthermal processes. The large
velocity dispersion and possible slight redshift of the OVII absorption (as
well as limits on the absorber's temperature and density) may be indicative of
a local intergalactic medium origin, though absorption from a hot, low-density
Galactic corona cannot be ruled out.
