Quasistatic measurements of room-temperature anelastic relaxation were used to characterize the properties of shear transformation zones (STZs) in amorphous Al 86.8 Ni 3.7 Y 9.5 in the dilute limit. Using a combination of nanoindenter cantilever bending and mandrel bend relaxation techniques, anelastic relaxation was measured over times ranging from 1 s to 3 Â 10 7 s. Direct spectrum analysis yields relaxation-time spectra, which display seven distinct peaks. The results were analyzed using a linear dashpot-and-spring model, combined with transition-state theory, to yield several STZ properties. These reveal a quantized hierarchy of STZs that differ from each other by one atomic volume. Potential STZs occupy a large volume fraction of the solid. They access their ergodic space, with the ratio of forward-to backward jump rates ranging from 1.03 to 4.3 for the range of stress values used.