During the summer of 1980, twenty post burn and two unburned coreholes were drilling into retort 16 at the Geokinetics field site in a jointly funded project by the DOE and the US EPA. The purpose of this investigation is to determine the physical, chemical, and mineralogical characteristics of retorted oil shale in a Geokinetics retort. Lithologic description and Fisher assay of the cores indicate that a complex pattern of six distinct zones was created by the process. Zone A is undisturbed rock, zone B has blast fractures, zone C shows slight alteration along fractures, zone D is blackened retorted shale, zone E is pastel colors representing higher temperatures, and zone F melted rock. The boundary of retorted shale is between zones C and D. Many factors control the formation of these zones.