  On the basis of a recently derived color-metallicity relation and stellar
parameters from the Sloan Digtal Sky Survey Data Release 7 spectroscopic
survey, a large sample of red horizontal branch candidates have been selected
to serve as standard candles. The metallicity and kinematic distributions of
these stars indicate that they mainly originate from the thick-disk and the
halo populations. The typical thick disk is characterized by the first group
peaking at [Fe/H] ~ -0.6, Vrot ~ 170 km/s with a vertical scale height around
|Z| ~ 1.2 kpc, while stars with [Fe/H] < -0.9 are dominated by the halo
population. Two sub-populations of the halo are suggested by the RHB stars
peaking at [Fe/H] ~-1.3: one component with Vrot > 0 km/s (Halo I) shows a sign
of metallicity gradient in the [Fe/H] versus |Z| diagram, while the other with
Vrot < 0 km/s (Halo II) does not. The Halo I mainly clumps at the inner halo
with R < 10 kpc and the Halo II comes both from the inner halo with R < 10 kpc
and the outer halo with R > 10 kpc based on the star distribution in the R
versus |Z| diagram.
