Low-frequency climate oscillations of the Colorado Plateau region are investigated with evolutionary spectral analysis to observe temporal changes in the power spectra of 12 drought-sensitive tree ring chronologies. The power spectra show large temporal and spatial variability. Several oscillations are simultaneously present at the majority of sites, indicating a high probability that the oscillations are related to regional climate phenomena. Most of the oscillations are of short duration, with periods of 20 to 80 years. The large temporal and spatial variability of the oscillations limits their usefulness in predictive models. The observed abrupt changes in power spectra suggest chaotic behavior and may represent a reordering of the processes influencing climate. A solar-climate interaction is suggested by a close correspondence between times of low sunspot activity and abrupt changes in the power spectrum observed in the chronologies. ¿ American Geophysical Union 1992