The continuous miner operator and a continuous miner helper had started a sump on the left side of #3 entry inby #16 cross cut of the pillar being mined in the 5th left C retreat mining section, MMU 001-0. One shuttle car had been mined, between shuttle cars the second shuttle car operator found the continuous miner had been caved on. In investigating the shuttle car operator found that the miner operator and miner helper were under a slab of roof rock that had fallen and trapped both miners. The rock had fallen and was leaning on the continuous mining machine.