A right to left sequence of pillaring was being used on the 4-LT off a west panel. The first lift was mined from the no. 2 pillar and the mining machine backed out of the lift. The two MRSs were being positioned for the next lift when a rock fell thru the 1st lift and across the entry in front of the MRSs. The fall was 25' long, 4' wide & 8' high & located 50' inby SS 1307.