We have conducted an extensive study of the evolution of surface morphology of single crystal diamond surfaces during sputtering by 20 keV Ga+ and Ga++H2O. We observe the formation of well-ordered ripples on the surface for angles of incidence between 40 and 70 degrees. We have also measured sputter yields as a function of angle of incidence, and ripple wavelength and amplitude dependence on angle of incidence and ion fluence. Smooth surface morphology is observed for < 40 degrees, and a transition to a step-and-terrace structure is observed for > 70 degrees. The formation and evolution of well-ordered surface ripples is well characterized by the model of Bradley and Harper, where sputter-induced roughening is balanced by surface transport smoothing. Smoothing is consistent with an ion-induced viscous relaxation mechanism. Ripple amplitude saturates at high ion fluence, confirming the effect of nonlinear processes. Differences between Ga+ and Ga++H2O in ripple wavelength, amplitude, and time to saturation of amplitude are consistent with the increased sputter yield observed for Ga++H2O. For angle of incidence < 40 degrees, an ion bombardment-induced "atomic drift" mechanism for surface smoothing may be responsible for suppression of ripple formation. For Ga++H2O, we observe anomalous formation of very large amplitude and wavelength, poorly ordered surface ridges for angle of incidence near 40 degrees. Finally, we observe that ripple initiation on smooth surfaces can take place by initial stochastic roughening followed by evolution of increasingly well-ordered ripples. (c) 2005 American Vacuum Society.