The reserve covers an area of 1195.14 km2, including 590.56 km2 in El Salvador,[1] 221.79 km2 in Guatemala,[2] and 382.79 km2 in Honduras.

[5] The reserve protects Montecristo massif, a highland area isolated from other mountains.

The massif is in the upper basin of the Lempa River, which drains into the Pacific Ocean.

[6] The biosphere reserve was created to protect the Montecristo cloud forest and its rare flora and fauna.

[6] The dense cloud forest of oak and laurel trees, which grow up to 30 meters high, houses rare wildlife species like the two-fingered anteater, striped owls, toucans, agoutis, pumas, and spider monkeys.