The difference between the temperature of the ocean at 4-cm and 2-m depth was continuously monitored during a cruise to the coastal transition zone off Point arena, California (38¿58'N, 123¿45'W), during June 1987. The two temperatures were coincident most of the time but diverged during one nearshore leg of the cruise where large temperature differences (ΔT) of up to 4.7 ¿C were observed between the 4-cm and 2-m sensors, in areas which were separated by regions where the two temperatures were coincident as usual. The spatial scale of this ''patchy'' thermal structure was about 5--10 km. The Naval Postgraduate School mixed layer model (Garwood, 1977) was used to simulate the near surface stratification when forced by the observed wind stress, surface heating, and optical clarity of the water. The model produced a thin strongly stratified surface layer at stations where exceptionally high turbidity was observed but did not produce such features otherwise. This simple model could not explain the horizontal patchiness in the thermal structure, which was likely due to patchines in the near-surface chlorophyll distributions or to submesoscale variability of the surface wind stress. ¿ American Geophysical Union 1991