Remote sensing is useful for studying certain oceanographic problems only if the signal obtained from the sea surface contains information about subsurface structure. Historical bottle temperature data from the California Current were analyzed for surface manifestations of vertical structure and subsurface mesoscale structure. Results showed that subsurface temperature is useful in predicting thermoclinic strength over a large area south of Poin Conception: the error of a regression estimate is 20--30% less than the error of the seasonal mean. However, surface temperature gives little useful information about mixed layer depth. Mesoscale patterns of temperature at the surface and at depth (caused by eddies, meanders and upwelling) are coherent (r2>0.50) to a depth below the mixed layer only off central California and Point Conception and along the coast of Baja California. Coherence is most likely to extend below the mixed layer during summer, when the water column is strongly stratified and the mixed layer is most shallow. Thus some aspects of subsurface structure, within limited regions of the California Current, have surface manifestations potentially detectable by satellite sensors. ¿ American Geophysical Union 1988