Aerial photographs showing strong refraction of swell near the northern California coastline were obtained on September 8, 1982. The possibility that this refraction is due to a large horizontal current shear is discussed; a maximum shear value of the order of 10-3 s-1, with the velocity directed along a linear slick-like front, is calculated from the wave data in the photo. In situ current data obtained at 90 m depth at a nearby midshelf site on two surface moorings separated by 390 m also show occasional periods of large horizontal velocity shear. On January 4, 1982, a maximum horizontal shear of order 10-3 s-1 was observed for several hours. These separate observations taken together indicate that large horizontal surface velocity shears of order 10-3 s-1 occur over the northern California continental shelf, and that large surface current shear can be usefully detected and measured by high flying high resolution sensors.