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as a response to the Andean deformation in the southern part of the CentralAndes. The Miocene Vinchina Formation (Turner, 1964) was deposited mainlyin fluvial, fluvial-eolian, eolian, and lacustrine environments, reaching up to6400 m in thickness representing the main depositional unit in the basin. Thisunit is remarkably exposed along the Sierra de Los Colorados (La Rioja Province,Argentina), where this study was carried out.The results from statistical analyses from 33 gravel beds, their modalcompositions, compositional trends, and distribution patterns, based on in-situlithological clast-counting, are presented. The statistical approach was carriedout by using hierarchical clustering and principal components analysis (PCA),which permitted differentiating three compositional clusters thought to representdifferent petrofacies. The first cluster involves samples with compositions widelydominated by neovolcanic andesitic clasts, where intrabasinal volcanic effusionswere the main detrital source. The second one comprises samples with mixedcompositions dominated by paleovolcanic clasts. Detrital sources of this clusterwere primarily the cordilleran/precordilleran area, with subordinated contributionsfrom the Western Sierras Pampeanas crystalline basement and intrabasinalvolcanic deposits. The third cluster involves mixed samples with a dominanceof crystalline-basement supply. The main source area for these samples was theWestern Sierras Pampeanas, although the cordilleran/precordilleran supply ispresent in significant proportions.This study illustrates the merit of using non-parametric statistics in provenancestudies, especially to detect internal compositional variations when multiplesource areas are active.