Nonetheless, the 50,150 hectares that comprise the park actually contain a variety of other fascinating ecosystems and on the 10-hour hike to the shelters on top of the mountain one passes through lower montane rain forest and montane rain forest, before finally emerging into subalpine rain paramo. The high humidity and abundant precipitation foster the luxuriant growth of mosses, bromeliads, and other epiphytes on the trunks and branches of the forest trees, of which the predominant species are several types of truly majestic live oaks (Quercus spp.).

As the tree line is neared, the vegetation becomes more and more stunted until at an elevation of about 3,300 meters the paramo begins. This is a conglomeration of low-growing plants that have evolved various adaptations for dealing with the harsh climate at the summit which is characterized by intense ultraviolet radiation, abrupt temperature change, high rainfall, and frequent frosts.

But don't despair, the weather could be worse! Ample geologic evidence is present on the summit of the Chirripó massif to indicate that some 25,000 years ago the area was covered by glacial ice. This glacier formed during the last of the Great Ice Ages when much of the northern hemisphere was also beneath ice, although the Chirripó glacier was not connected to those glaciers. A dozen or more small glacial lakes, piles of rounded rocks (moraines), and U-shaped valleys are all mute testimony to the existence of the former ice cover.