LANCASTER — The 192-year-old Rock Mill is preparing to return to life as a working gristmill, grinding corn and wheat into meal and flour to demonstrate Fairfield County’s agricultural heritage. The water-powered mill perched on sandstone cliffs overlooking the Hocking River is expected to start grinding grain by Thanksgiving.adcelannotate = {"mobilepaywallcategory" : "MOBILE_PREM-LOCAL","nativepaywallcategory" : "NATIVE_PREM-LOCAL"};