A packet of high-frequency (period ~8 min) internal gravity waves was observed on a precision depth recorder (PDR) chart while and anchor station was being conducted during the Cue 1 experiment off Oregon. The anchor station was located over the continental shelf and in the frontal zone associated with coastal upwelling. The packet appeared as a set of three oscillations (maximum peak-to-peak amplitude of 11 m) of a scattering layer located at a depth of about 20 m, which was immediately below the center of the permanent pycnocline (25.5-26.0 sigma &tgr;) at that time and location (water depth 80 m, 10-km off-shore). The scattering layer occurred at the depth of a chlorophyll A maximum; strong temperature, salinity, and sound speed gradients; and strong vertical shear of the horizontal velocity. Simultaneously, a series of surface slicks, oriented parallel to the isobaths and propagating onshore, was observed under conditions of light winds. From the spacing of the slicks a horizontal scale of 100 m was estimated; this scale corresponded most nearly to the wavelength of the first internal wave mode for the observed wave period. From time series of nearby moored current and temperature sensors, bursts of high-frequency oscillations were noted to occur on semidiurnal tidal cycles. Such bursts had occurred a few hours before the internal wave packet was observed on the PDR. It is concluded that the semidiurnal baroclinic tide breaks down in the frontal zone off Oregon, forming large-amplitude high-frequency internal gravity waves. These waves can induce detectable surface slicks under light wind conditions and major perturbations of a shallow scattering layer when it is present.