Five earthquakes from the Gulf of California, recorded at the John W. Kidd Memorial Seismological Observatory of The University of Texas at El Paso, are analyzed to estimate the thickness of the sedimentary layer of the Sonoran Embayment located southwest of El Paso, Texas and bounded on the western extremity by the Sierra Madre Occidental. The seismograms are digitized at -sec intervals and filtered in the time domain with a Parzen lag window to regenerate the fundamental-mode Rayleigh waves. Arrival times of these short-period surface waves are reduced to the time required to propagate through the Sonoran Embayment. The data are studied by Savarensky's method and by spectral analysis to yield group-velocity dispersion values. The results of the two distinct methods agree well. Theoretically obtained dispersion curves, in which the indexing parameter is layer thickness, are fitted to the velocity dispersion points. It is found that the sedimentary layer of the Sonoran Embayment is 2 to 3 km thick.