at the southern end of the sierra de la higuera, northern of mendoza's precordillera, crops out an eopaleozoic succession tectonically affected. this is represented by an n-s strip of limestone that dips to the west and is partly folded. it is assigned to the san juan formation (lower ordovician). the maximum thicknesses of the carbonate deposits are about a 70 meters. the conodont fauna of the middle and upper part of the section suggests a floian age. the carbonate sequence was interpreted on microfacies terms according to textural, compositional, fossiliferous and diagenetic features. it has been recognized the following microfacies: mudstones, bioclastic-pelletoidal wackestones, packstones with intraclasts, grainstones, crinoidal grainstones and rudstones. at the lower member there are sedimentary structures that indicate low to medium energy. in the upper member, the lower section is characterized by microfacies showing a strong mechanical distribution of bioclasts, suggesting sedimentary structures associates with me- dium to high energy. towards the top, carbonate microfacies reflect low energy (mudstones, and pelletoidal wackestones). the san juan formation is transitionally underlying with a mixed carbonate-shally unit of dark colors, six meters thick, which can be interpreted as the gualcamayo formation (floian-dapingian).