The geography of the Colombian side is dominated primarily by the river delta of the Atrato River, which creates a flat marshland at least wide, half of this being swampland. The Serranía del Baudó range extends along Colombia's Pacific coast and into Panama. The Panamanian side, in sharp contrast, is a mountainous rainforest, with terrain reaching from in the valley floors to at the tallest peak (Cerro Tacarcuna, in the Serranía del Darién).