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The Guarco valley is known for being ah intermountain depression which has been overfilled by volcanic products (i.e. debris flows, debris avalanches, lava flows) and volcano-sedimentary products (coluvial, fluvial and lake deposits) from Irazú volcano as well as from the adjacent Tertiary sedimentary and volcanic mountain ranges. A lithological correlation was established, based on the interpretation of 85 boreholes (all within depths of 31 to 200 m). This correlation was established for three sectors, one to the west, other to the east and one at the central zone of the city of Cartago. The western sector showed a sedimentary basement of Miocene rocks, overlain by a series of lava flows ∼18 m thick. These lavas are overlain by at least 4 different events of alternated lahars and debris avalanches with a total thickness of 67 m, separated by lenses of clays, which can be interpreted as paleosols. The top of the epiclastic sequence corresponds to a 6000 years old lacustrine and a debris avalanche deposit closing the Holocene. The central sector shows at the basement a series of lava flows 52 m thick, overlaid by 130 m thick laharic deposits. The eastern sector has up to 46 m thick lahar deposits overlain by 75 m of lava flows that are covered by lahars as well. At the top of the sequence, the distal facies of the Reventado debris avalanche are found, and they are restricted to the western sector and historic lahars mainly on rivers channels. The stratigrafic correlations show the existence of buried lava flows that are much more extensive than the morphology suggest, as well as the filling-up of the Middle to Upper Pleistocene basin with epiclastic products. Based on the stratigraphy and correlations with paleomastozoological founds, it can be interpreted that the Upper Pleistocene deposits (?) are at a very shallow depth in the southern part of the valley, while to the east, the Holocene deposits are dominant. Also, the stratigrafic profiles confirm the presence of the Aguacaliente Fault System that cuts through El Guarco Valley. [ABSTRACT FROM AUTHOR]