AbstractIn order to acquire information about the dynamics of internal movement of a rock glacier, the three-dimensional eigenvalue technique was applied to the fabric analysis of 13 samples of clasts from a vertical section in a 15 m deep trench in this landform on Mt. Mestas, Colorado, U.S.A. The eigenvalue analysis of dip and directional data from platy felsite clasts revealed that the mean direction of the clasts was oriented transverse to the downslope direction. A two-axis plot of the ratios of normalized eigenvalues illustrated that the fabric could be identified as strong clusters although weak girdles were also detected. By combining samples 1–6, 7–9, 10–13, respectively, and comparing their mean dip of the clasts relative to the surface angle reveals three trends. Two hypotheses were posed to explain the cyclic data: (1) three temporally, distinct, catastrophic debris flows contributed to the development of the rock glacier, and/or (2) the three groups of samples can be attributed to internal shear planes.