One hundred and seventy pairs of temperature and light transmission profiles were obtained by simultaneous conductivity-temperature-depth (CTD) and light transmissometer casts in three cruises on the R/V Yaquina over the continental shelf off Oregon. These were analyzed for bottom nepheloid layers (BNL) and bottom mixed layers (BML). Supplementing these data were 1177 CTD profiles taken during the Coastal Upwelling Ecosystems Analysis (Cuea) program and time series current data obtained under the Winter-Spring Transition Experiment on the Oregon Continental Shelf program. Frequencies of BML occurrences obtained from Cuea data taken during July and August 1972 and July and August 1973 were 52.9 and 53.3% for the respective years. Frequency of BNL occurrences for each of the three Yaquina cruises was consistently higher than that of BML. Large temporal variations in bottom layers are attributed to advection of different water types there. Frequency of BNL and BML is clearly associated with coastal upwelling intensities; under intense coastal upwelling, BNL and BML tend to be dissipated, and under weak coastal upwelling, they tend to be thick.