The Andes is practically a coastal mountain range, however there is a narrow strip of plains separating the Andes from the Ocean. This plains are crossed by some short yet caudalous rivers, like the Guayas River in Ecuador, and the Baudo, San Juan and Patía Rivers in Colombia.
The Choco Valley is a plain area defined by two main rivers, the Atrato that runs northwards to the Caribbean, and the San Juan, which ends in the Pacific. Next to Cherrapunji in India, this is the second rainiest spot in the world. The Valley is surrounded by the Andes in the East and the Baudo mountains in the West. The Baudo mountains are a low yet rainy coastal range.
South of the San Juan there is a series of plains crossed by rivers and "esteros" and covered by forest.