Yandang Mountains were formed through volcanic activity during the
Cretaceous period -120 million years (Ma) ago. Similar igneous rocks are widespread in SE China, forming a ~ wide and ~ long belt of volcanic-intrusive complexes. Yandangshan
caldera is a round
volcanic‐
intrusive complex with a diameter of , of which the north-east part was destroyed by a later regional fault. The mountain shows often conspicuous layering corresponding to the four different episodes of eruptions, giving rise to terrace-like structures where flatter, forested areas are separated by vertical cliffs. Mt. Yandang is mostly covered by deciduous and evergreen forests, mixed with some
Cunninghamia. Drier ridges can be dominated by small
pine trees. There are also some bamboo grooves. Lower slopes and valleys are used for agricultural purposes, for example for growing tea, or as fruit gardens. Herbs and mushrooms collected from the mountain are sold locally. A number of plant and animal species have been named after Mt. Yandang. A species of sedge,
Carex yandangshanica, has been described from Mt. Yandang and two other mountainous locations in
Zhejiang. Mt. Yandang has also given its name to
Cyclosorus yandangensis, a marsh fern, and
Arachniodes yandangshanensis, a holly fern. Among animal species, a mite
Eustigmaeus yandangensis has been named after Mt. Yandang, but this has been challenged. Yandang Mountains are everywhere influenced by human activity; there is an extensive network of official tourist paths, clearings for fire-prevention, and unofficial paths used by the local people for collecting resources from the mountains; nevertheless, because of the steep terrain, some parts are difficult to access. Whatever wildlife survives tends to be very elusive. Notable inhabitants of Yandang Mountains include
Cabot's tragopan, a nationally protected species in China.
Chinese pangolin is also reported to live in Yandang Mountains. Yandang Mountains have been considered as one of the areas where
South China tiger might still persist, but there is no positive evidence and the species is considered functionally extinct in the wild. ==Cultural significance==