The mountains climb from, with many large and deep ravines. They are formed of folded sedimentary rocks with series of younger granitic intrusions that date from the Palaeozoic to Cenozoic, with the majority being Mesozoic. The climate is subtropical in the lower regions and temperate and subhumid above, with average temperature from 16° to 20° C. There is regular frost in the higher mountains. Annual rainfall, fed by the trade winds from the Caribbean sea, ranges from or more. The Valle Nacional River originates in the Sierra de Juárez, one of the major tributaries of the Papaloapan River.
Vegetation
The Sierra Juárez is one of Oaxaca State's wettest areas and richest in forest diversity, with perhaps 2,000 of the 8,000 or more plant species that are found in the state. It is mostly covered by montane cloud forest, but includes tropical evergreen forests and forests of pine, pine-oak and oak. The cloud forest forms a band from in height, up to along the northern and eastern slopes. The climate is cool, 14°-20° C, and has mean annual rainfall that exceeds and is sometimes much higher. The dominant trees are tall and include evergreen and deciduous species, palms, tree ferns, heather shrubs, vines, and moisture-loving herbs. The tropical evergreen forest is dominated by evergreen trees tall, with abundant lianas and tropical epiphytes. Pine and pine-oak forests, at a height from have evergreen trees tall, with grasses dominating the lower stratum. Oak forests at a height from grow in areas with relatively lower rainfall that have a dry season in summer. The oak forests are found in the western, inland part of the sierra to the Rio Grande Basin.
The Sierra Juárez is the land of the Sierra Zapotecs, of whom President Benito Juárez was one of the most famous. The Zapotecs of the Sierra Norte, who call themselves the bene xon, are one of three major Zapotec regions in southern Mexico. The other three reside in the Isthmus of Tehuantepec, the Valles Centrales region and the Sierra Madre Oriental. The bene xon divide into four sub-cultures: Cajonos, El Rincón, Ixtlán and Choapan. Other indigenous people include the Chinantec, Mixe and Mixtec.
Environmental concerns
The Sierra Juárez is home to threatened mammals such as jaguar, ocelot, and brocket deer. It is also a habitat for the threatened dwarf jay, and is the richest region in Mexico for butterflies. It is under stress from logging, agriculture, grazing, and colonization, and is potentially threatened by hydroelectric dams. There is no official plan to establish nature reserves. However, the region promotes ecotourism to help preserve the biosphere with various enterprises offering cabins, camping, access and guides for hiking and mountain-biking trails, horseback riding, bird-watching, and cave exploration.
