  We present an analysis of high-resolution far-ultraviolet archival spectra
obtained with the Space Telescope Imaging Spectrograph on the Hubble Space
Telescope of the star HD 75309, which probes high-velocity shocked gas in the
Vela supernova remnant (SNR). We examine high-velocity features from
intrinsically strong absorption lines of O I, Si II, Si II*, C II, C II*, and
Si III. We also detect high-velocity components in the N V doublet and compare
these features to observations of high-velocity O VI absorption, available from
archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are
derived from the observed fractional abundances of the various ions, while gas
densities and thermal pressures are obtained from the relative populations in
excited fine-structure levels of C II and Si II. Our results indicate that the
highly ionized species at high velocity probe gas in a region immediately
behind a shock driven into an interstellar cloud, while the lower ionization
species trace material further downstream in the cooling region of the
post-shock flow. Low velocity N V and O VI absorption may trace gas in a
conductive boundary layer between the unshocked portion of the cloud and the
hot X-ray emitting intercloud medium. Temporal variations in high velocity Ca
II absorption features observed toward HD 75309 further confirm the highly
inhomogeneous nature of the interstellar medium interacting with the Vela SNR.
