The Sobo, Katamuki and Okue Biosphere Reserve also known as Sobokatakue Unesco Eco Park (祖母傾大崩ユネスコエコパーク, Sobokatamuki Okuzure yunesukoekopāku) was created in 2017.

[7][8] The landforms of the Biosphere Reserve are the heavily modified result of volcanic activity over the last 14 million years.

A massive eruption about 13.7 million years ago involved the Okueyama Volcano-plutonic Complex,[9] and measured 8.0 on the Volcanic Explosivity Index.

[10] Later, most recently about 90,000 years ago, mainly the lower lying land was modified by pyroclastic deposits from the Aso Caldera to the west whose eruption was 384 km3 (92 cu mi).

In the lower core and buffer areas the cover is by old-growth forest including Japanese beech and Tsuga.