As a part of the Second Coastal Upwelling Experiment along the Oregon Coast in summer 1973, extensive thermodynamic data were gathered in a mesoscale area. These data were examined in relation to the marine inversion at seven stations along a line from Salem, Ore., to a point 22 n mi off the coast, or a distance of approximately 65 n mi. The structure of the inversion was examined via time sections of temperature and potential temperature at each station, and cross sections along the line for selected times during the intensive period. Limited time and cross sections of relative humidity were also examined. The inversion seemed to respond to even weak synoptic-scale changes, rising with low-level convergence and lowering with subsidence in high-pressure regions. It was also found that the marine inversion had a more complex structure than a single stable layer.