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In the Bolivian Eastern Cordillera, continental evaporites occur in late Cretaceous and early Tertiary Formations (Aroifilla, Chaunaca, uppermost EI Molino, Santa-Lucia). Studies carried out in the Potosi basin show that these formations were deposited within an almost continuous lacustrine system subjected to large variations in hydrology independent of any significant marine contribution. Thus, in addition to tectonic effects, the hydrology was mainly governed by changes in the evaporation/precipitation ratio. Major evaporitic phases took place during arid periods which caused the contraction of the lakes and induced the formation of sub-perennial to ephemeral residual brine ponds trapped in the deep part of the lacustrine system (upper Aroifilla, middle Chaunaca, Santa-Lucia Formations). The crystallization of evaporitic minerals occurred as subaqueous precipitation in brine sheets and as interstitial growth both in the dry peripheral mud hats and in the central area when the water table fell below the sediment surface. Although the evaporite mineral assemblage only includes calcium sulfate, it is likely that more soluble salts may have crystallized and subsequently underwent a partial or total dissolution. The source ions were the catchment basin rocks with a probable contribution of reduced sulfur compounds of volcanic origin. Wide Variations of water redox conditions are substantiated by the isotopic composition of the sulfates. During wetter periods (Chaunaca p.p., El Molino), the expansion of the lacustrine system induced perennial conditions with slightly saline to freshwater although episodic desiccations may have occurred. The sedimentation is therefore characterized by decreasing evaporitic influences, carbonate sedimentation (shell coquinas, oolite/oncolite deposits, stromatolitic and thrombolitic buildups, organic-rich laminated carbonates, etc) and, the diversification of the fauna and flora in the lake waters and near the shorelines. Toward the top of the Fl Molino Formation, episodic prevalence of sodic alkaline waters induced the formation of analcime-rich laminites. The rise of the lake level was responsible for the sporadic development of seaward outflows by which marine organisms may have entered into the lacustrine system. This late Cretaceous-early Tertiary continental domain was located in the subtropical belt where aridity and sub-desertic conditions alternated with more humid periods.