Most of the park is low alluvial floodplain (sea level to 20m) which extends far inland, and is occasionally interrupted by isolated volcanic hills of 100-300 m. An intricate network of blackwater canals and creeks dissect palm swamps and mixed rainforest throughout the region. The natural vegetation of the area progresses from the poorly-drained swamp forests in the lowlands near the coast to tropical wet and pre-montane forests further inland at higher elevations. Forest species composition gradually shifts from coastal scrub to huge expanses of Raphia palm swamp and mixed species along waterway margins, to tall multi-layered evergreen forests. Canopy trees may exceed 60 m in height with girths of 1-2 m, some with massive buttressing. Species diversity of both plants and animals is very high here -- among the highest in Costa Rica.