  We present the fourth of the Cholla Galactic OutfLow Simulations suite
(CGOLS). Using a physically-motivated prescription for clustered supernova
feedback, we successfully drive a multiphase outflow from a disk galaxy. The
high resolution ($< 5\,\mathrm{pc}$) across a relatively large domain
($20\,\mathrm{kpc}$) allows us to capture the hydrodynamic mixing and dynamical
interactions between the hot and cool ($T \sim 10^4\,\mathrm{K}$) phases in the
outflow, which in turn leads to direct evidence of a qualitatively new
mechanism for cool gas acceleration in galactic winds. We show that mixing of
momentum from the hot phase to the cool phase accelerates the cool gas to
$800\,\mathrm{km}\,\mathrm{s}^{-1}$ on kpc scales, with properties inconsistent
with the physical models of ram pressure acceleration or with bulk cooling from
the hot phase. The mixing process also affects the hot phase, modifying its
radial profiles of temperature, density, and velocity from the expectations of
radial supersonic flow. This mechanism provides a physical explanation for the
high velocity, blue shifted, low ionization absorption lines often observed in
the spectra of starburst and high redshift galaxies.
