Observations of high frequency internal waves were made from 1 to 14 December 1966, in the deep sea off Baja, California. The fluctuations of the depth of an isotherm were measured with a three-element horizontal array attached to a stable platform. The waves are characterized as a broad band phenomenon with a continuous distribution in frequency. For short intervals of time, a narrow frequency band within the continuum is adequately described as a horizontally plane wave of a single vertical mode. Furthermore, this simplified structure is stationary over time spans of several days. High modes are present in the low frequency waves. Above 4 cycles per hour, however, the first mode predominates. The spectral shape is consistent with the shear limited equilibrium spectrum proposed by Phillips (1966). In addition, the predominance of the first mode at high frequencies further emphasizes the importance of shear instability in internal wave propagation. The horizontal properties of the wave field indicate well-defined directions of narrow-band propagation. These directions and the dispersive properties of the propagation have led to the identification of local topographic features in generating areas of internal waves. (Author).