  We have studied a sample of 415 associated (z_ab z_em; relative velocity with
respect to QSO <3000km/s) Mg II absorption systems with 1.0<=z_ab<=1.86, in the
spectra of SDSS DR3 QSOs, to determine the dust content and ionization state in
the absorbers. We studied the dependence of these properties on the properties
of the QSOs and also, compared the properties with those of a similarly
selected sample of 809 intervening systems (apparent relative velocity with
respect to the QSO of >3000km/s), so as to understand their origin. From the
analysis of the composite spectra, as well as from the comparison of measured
equivalent widths in individual spectra, we conclude that the associated Mg II
absorbers have higher apparent ionization, measured by the strength of the C IV
absorption lines compared to the Mg II absorption lines, than the intervening
absorbers. The ionization so measured appears to be related to apparent
ejection velocity, being lower as the apparent ejection velocity is more and
more positive. There is clear evidence, from the composite spectra, for SMC
like dust attenuation in these systems; the 2175AA absorption feature is not
present. The extinction is almost twice that observed in the similarly selected
sample of intervening systems. We reconfirm that QSOs with non-zero FIRST radio
flux are intrinsically redder than the QSOs with no detection in the FIRST
survey. The incidence of associated Mg II systems in QSOs with non-zero FIRST
radio flux is 1.7 times that in the QSOs with no detection in the FIRST survey.
The associated absorbers in radio-detected QSOs which comprise about 12% of our
sample, cause 3 times more reddening than the associated absorbers in
radio-undetected QSOs. This excess reddening possibly suggests an intrinsic
nature for the associated absorbers in radio-detected QSOs.
