The studied area belongs to the Térraba basin. The stratigraphy is represented by the following units: The Tulín Formation is composed by gabbros and pillow lavas with geochemistry similar. The pillow lava has vesicular and microdolerite texture. There are basaltic lavas interbedded with epiclastic sediments. The age of this formation is Upper Cretaceous to Basal Eocene. Descartes Formation was defined by first time in this area. The formation is composed by interbedded sandstones and mudstones. The colors of the rocks are black, red and greenish pink. The strata beds are good with centimetric laminations, but they are massive strata beds; locally the sequence present hydrothermal alterations and the rocks become light green color. The age is Late Paleocene using the <span name="style_italic">Morozovella velascoensis</span> foraminifera. Caraigres Formation belongs to the Valle Central Basin. It is composed by interbedded sandstones and mudstones, with black and gray color, the volcanic influence is common. The age of the formation is Oligocene to Basal Miocene. The geologic contact between Caraigres Formation and Descartes formations probably transitional. Curré Formation is composed by fine and coarse black sandstones, mudstones and dark grey volcaniclastic conglomerates. The conglomerates has metric packages with good stratification or interbedded with sandstones. The age is Middle Miocene. Grifo Alto Formation consists of porphyritic andesites with plagioclases, pyroxenes, amphiboles phenocrysts and porphyritics basalts with augite. It is possible to find fine and coarse weathering tuffs, and hydrothermal alteration. The age of this formation is Pliocene to Pleistocene. Altos Chiral Lacustrines Deposits are defined by first time in this study like a new geologic unit. It is composed by orangized mudstones. It is not consolidated and it overlays Descartes Formation by angular unconformity. The outcrops are near Altos Chiral and Alto San Juan, to the west of San Marcos de Tarrazú. The age of this new unit probably is Plio-Pleistocene? Alluvial Terraces consist of alluvial deposits, with metric blocks of different kind of volcanic rocks. Some blocks have hydrothermal alteration. The outcrops are near San Marcos, Sta. María, Copey and Londres and Naranjito near Quepos. The study area presents a strong tectonic influence, the deformation started with reverse faults which were subsequently cut by transcurrent faults. The most important fault is Paquita-Chonetera fault, which expose the Descartes Formation. foraminifera. Caraigres Formation belongs to the Valle Central Basin. It is composed by interbedded sandstones and mudstones, with black and gray color, the volcanic influence is common. The age of the formation is Oligocene to Basal Miocene. The geologic contact between Caraigres Formation and Descartes formations probably transitional. Curré Formation is composed by fine and coarse black sandstones, mudstones and dark grey volcaniclastic conglomerates. The conglomerates has metric packages with good stratification or interbedded with sandstones. The age is Middle Miocene. Grifo Alto Formation consists of porphyritic andesites with plagioclases, pyroxenes, amphiboles phenocrysts and porphyritics basalts with augite. It is possible to find fine and coarse weathering tuffs, and hydrothermal alteration. The age of this formation is Pliocene to Pleistocene. Altos Chiral Lacustrines Deposits are defined by first time in this study like a new geologic unit. It is composed by orangized mudstones. It is not consolidated and it overlays Descartes Formation by angular unconformity. The outcrops are near Altos Chiral and Alto San Juan, to the west of San Marcos de Tarrazú. The age of this new unit probably is Plio-Pleistocene? Alluvial Terraces consist of alluvial deposits, with metric blocks of different kind of volcanic rocks. Some blocks have hydrothermal alteration. The outcrops are near San Marcos, Sta. María, Copey and Londres and Naranjito near Quepos. The study area presents a strong tectonic influence, the deformation started with reverse faults which were subsequently cut by transcurrent faults. The most important fault is Paquita-Chonetera fault, which expose the Descartes Formation.

Dota; Formación Descartes; Formación Curré; Terrazas aluviales; Depósitos Lacustres Altos Chiral; tectónica; Falla Paquita-Chonetera; sistema de fallas; Paleoceno; Mioceno; Morozovella velascoensis