  We present an echelle spectrum of the Swift GRB 050730, obtained four hours
after the burst using the MIKE spectrograph on the Magellan Clay Telescope when
the afterglow was at R=17.7. The spectrum reveals a forest of absorption
features superimposed on a simple power-law shaped continuum, best described as
f_nu(lambda)\propto lambda^{alpha} with alpha =1.88\pm 0.01 over
lambda=7000-9000 A. We identify the GRB host at z_GRB=3.96855 based on the
hydrogen Lyman absorption series, narrow absorption lines due to heavy ions
such as OI, CII, SiII, SII, NiII, FeII, CIV, SiIV, and NV, and fine structure
transitions such as OI*, OI**, SiII*, CII*, and FeII*. Together these
transitions allow us to study the the properties of the interstellar medium
(ISM) in the GRB host. The principal results are as follows. (1) We estimate a
neutral hydrogen column density of log N(HI)=22.15\pm 0.05 in the host. (2) The
associated metal lines exhibit multiple components over a velocity range of ~80
km/s, with >90% of the neutral gas confined in 20 km/s. (3) Comparisons between
different ionic transitions show that the host has little/no dust depletion and
has 1/100 solar metallicity. (4) The absorbing gas has much higher density than
that of intervening damped Lya absorption (DLA) systems. In addition, we report
the identification of an intervening DLA system at z_DLA=3.56439 with log
N(HI)=20.3\pm 0.1 and < 5% solar metallicity, a Lyman limit system at
z_LLS=3.02209 with log N(HI)=19.9\pm 0.1, a strong MgII absorber at
z_MgII=2.25313, and a pair of MgII absorbers at z_MgII=1.7731, 57 km/s apart.
We demonstrate that rapid echelle spectroscopy of GRB afterglows helps to
reveal a wealth of information in the ISM and the intergalactic medium along
the sightline (abridged).
