  We study the nonequilibrium phase transition in a contact process with
extended quenched defects by means of Monte-Carlo simulations. We find that the
spatial disorder correlations dramatically increase the effects of the
impurities. As a result, the sharp phase transition is completely destroyed by
smearing. This is caused by effects similar to but stronger than the usual
Griffiths phenomena, viz., rare strongly coupled spatial regions can undergo
the phase transition independently from the bulk system. We determine both the
stationary density in the vicinity of the smeared transition and its time
evolution, and we compare the simulation results to a recent theory based on
extremal statistics.
