La Pacana has a diameter of with a north-south elongation. This is one of the best exposed and largest calderas in the world; the largest caldera known is Toba in Sumatra with a maximum length of . La Pacana might not be a single caldera; some reconstructions imply that the northern parts of the caldera are actually a separate collapse structure. The floor of the caldera lies at an elevation of , the central uplift and the caldera rim are higher and reach . The caldera rim is well exposed except in the northern and western sides, where later volcanism has buried it. After the formation of the caldera, sediments and tuffs within the caldera were uplifted over an angular area of , forming the high resurgent dome known as Cordón La Pacana. This resurgent dome is cut by numerous faults and features a poorly developed graben on its summit. Originally it was believed that the present-day calder rim did not coincide with the caldera ring fault, which was instead identified to coincide with margins of the resurgent dome; later research however indicates the present-day topographic margin as the caldera edge. The resurgent dome is separated from the caldera rim by a wide moat that makes up about two thirds of the entire surface of the caldera, but is interrupted on the northern side of the caldera by the hinge of the caldera collapse, which assumed the form of a trap-door. The moat is filled by sediments formed by erosion and by alluvial, evaporite and lacustrine sediments left behind by lakes.