Reflectances of Eocene vitrinite from a wide selection of sites in southern British Columbia show a concentration between 0.45 and ~1.0%. Localities with reflectances less than 0.45% may be less deeply buried (Kamloops at 0.25%) than most of the others, younger (Hat Creek), or perhaps associated with an abnormally low geothermal gradient (Princeton?). Localities with abnormally high reflectances (>1.0%) include sites with local heat sources, such as an intrusion (Afton mine near Kamloops), a coal fire (Hat Creek), or a hot, pyroclastic flow (south of Princeton). Other occurrences with high reflectances are those that may have been blanketed by an overthrust sheet (Big Bar), deposited on crustal rocks shortly after they had been tectonically stripped and while they were still warm (Enderby), or otherwise juxtaposed against such deep crustal rocks (White Lake area). Measurement of reflectance plays a useful role in calling attention to abnormal geothermal conditions once the regional pattern is determined.