We estimate the attenuation around Cajon Pass, southern California, for frequencies above 10 Hz, and we find total Q to exhibit only weak frequency dependence, ranging from ~800 at 10 Hz to ~1500 at 100 Hz. The intrinsic attenuation is approximately twice the level of the scattering attenuation. Measurements are made using earthquake seismograms recorded at 0--3 km depth using the multiple lapse time window method. The results are not dependent on receiver depth and are consistent with previous estimates of Q made from direct waves recorded at 2.5 km depth. Our Q values are therefore thought to be representative of the seismogenic crust, and the technique used is uncontaminated by the highly attenuating near surface, at least above ~10 Hz. We also calculate Q from surface data between 1 and 10 Hz and find a clear change in the frequency dependence of both intrinsic and scattering attenuation at ~10 Hz. Q exhibits strong frequency dependence below 10 Hz (∝f1.8), consistent with previous studies in active tectonic regions, and only weak frequency dependence at higher frequencies (∝f0.34). This change in behavior renders it unwise to extrapolate Q measurements outside the frequency range from which they were derived, for example, in earthquake source studies. Possible factors responsible for the apparent change in frequency dependence of Q are considered. Further work is required, however, to resolve the causes of this change. ¿ 1998 American Geophysical Union