A relatively complete section of Ordovician to Permo-Carboniferous and Cretaceous-Tertiary formations is exposed in the Yapacani headwater region. Fold axes in the immediate area trend N.40 degrees W., swinging to nearly north-south farther to the southeast and to a more westerly trend west of the river. Bending is attributed to the effects of left-lateral displacement along the postulated Ichilo fault zone, of which the Colorado strike-slip fault in the Yapacani area is considered the southernmost branch.

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