Surface gamma-ray logs or scintillometer profiles of measured sections provide an excellent correlation tool in frontier areas where well control is sparse but outcrops are abundant. Subtle changes in lithology are commonly detected by surface gamma-ray measurements. Furthermore, gamma-ray measurements across concealed strata may give clues to the lithology of the buried rock. A portable scintillation counter is used in conjunction with lithologic descriptions. Five-foot stratigraphic intervals provide optimum results. Surface gamma-ray logs have been successfully used to correlate and trace Paleozoic and Mesozoic units in Nevada, Utah, and Kentucky.--Modified journal abstract.