The ecoregion occupies the eastern spine of the central Andes, covering 10.2 million hectares - about 25 million acres, or roughly the area of Iceland. In Colombia it runs along the southern Cordillera Oriental. In Ecuador it drapes the eastern face of the Cordillera Real. In Peru it continues down the northern Andes, where an unusual geographic twist extends part of the ecoregion onto the Pacific slope. To the north it fades into the Magdalena Valley and Cordillera Oriental montane forests. On its lower edge it merges into Napo moist forest to the east and Northwestern Andean montane forest to the west. Its upper boundary brushes Northern Andean paramo and Cordillera Central paramo. The southern end trails into the drier Maranon and Tumbes-Piura forests.

Near the southern end of the ecoregion the Andes nearly break. The Huancabamba Depression is the lowest pass in the entire Andean chain - about 2,000 meters above sea level - and it functions as a biological bridge between worlds. Species from the Amazon can cross here into the Pacific lowlands; Pacific species can climb east into the rainforest. The consequences for evolution have been profound. The depression has concentrated endemism, accelerated speciation, and shaped the flora and fauna of the surrounding forests into a mix that has elements of Amazon, Pacific-dry, and Inter-Andean ecosystems. The Cajamarca Region of Peru, straddling the depression, is one of the most endemism-rich zones in the whole ecoregion. The mountains north and south of the gap formed on different geological clocks - Miocene origins for the southern mountains, Pliocene to Pleistocene for the northern.

The vegetation reads like a vertical ecology textbook. At the lower elevations the ceja de montana (eyebrow of the mountain) is a closed, exuberant forest where trees grow tall and the canopy absorbs almost all the light. Climb higher and the trees shrink. The air cools. Mist condenses on leaves as reliably as rain falls, and the cloud forest begins - branches dripping with bromeliads, orchids in improbable shapes, mosses a foot deep on every horizontal surface. Higher still, wind and cold push the trees into elfin forest: knee-high, twisted, blanketed in lichen, each tree a bonsai sculpted by decades of fog. Specialization is extreme. Many species occupy altitude bands only a few hundred meters thick, and plants that cannot cross a ridge or valley become endemic simply through physical isolation.

The mammal list reads like a Latin American fever dream: Venezuelan red howler monkeys, white-fronted capuchins, the critically endangered yellow-tailed woolly monkey, spectacled bears - the only bear species in South America - taruca deer, guanacos in the drier zones, kinkajous, and possibly the mountain tapir. A 1982 study of bats found that 37 percent of the species on the western slopes were endemic. Endangered mammals include the equatorial dog-faced bat, the giant otter in the lower river systems, the mountain tapir, and the white-bellied spider monkey. Bird life includes masked mountain tanagers, chestnut-bellied cotingas, cinnamon screech owls, neblina metaltails, and the unmistakable Andean condor drifting on thermals. Endangered endemics include the white-breasted parakeet, the coppery-chested jacamar, the bicolored antvireo, the royal sunangel, and the black-and-chestnut eagle.

The most striking biodiversity in the Eastern Cordillera Real may be amphibian. Scientists have catalogued dozens of endangered frogs in the ecoregion - Kingsbury's rocket frog, multiple Atelopus stubfoot toads, glass frogs you can see the heart beat through, Pristimantis robber frogs by the dozen, water frogs specialized to single valleys. The genus Pristimantis alone accounts for many of the endangered species; these small terrestrial frogs skip the tadpole stage entirely, laying eggs that hatch as tiny froglets. The specializations make them exquisitely vulnerable to habitat loss. The World Wide Fund for Nature lists the ecoregion as "Vulnerable." The forest is accessible - too accessible. Commercial logging of Podocarpus and Prumnopitys conifers has eaten into ancient stands. Large areas have been cleared for pasture and subsistence farming. Protection rests on a handful of reserves: Cayambe Coca in Ecuador, Podocarpus National Park in the south, the Noroeste Biosphere Reserve, and whatever the steep terrain itself refuses to give up.