Phu Kao - Phu Phan Kham National Park, an area in upper northeastern plateau, locates in the lower part of Udon Thani Province and lupper part of Khon Kaen Province. The main geology of this area is mountains of sandstone, has sandstone stratum on the top layer of soil, has hard soil or sandy hard soil beneath, and has laterite and sandy soil scattering all over the area. There are plants, animals, and naturally beautiful scenery. The area consists of deciduous forest and is about 322 squares kilometers.

The appearance of Phu Kao looks like frying pan which has great plain in the center. It can be assumed that this area is the remains of a volcano extinguished millions of years ago, or layers of rock in this area bending up to being mountain ridges. Phu Kao Mountain Range is two peripheral lines of mountain; the outer line consists of high mountains; the inner line consists of lower mountains which its hillside is not much slope. Most of the area alternates between high and low, and some are plains.

Phu Phan Kham, in Phu Phan Mountain Range, is a long mountain range lying northeast and southwest. The southwest part was a lower vast-plain of Lam Nam Phong, the very big valley, which, after finished building Ubonratana Dam, is now a lake and becomes half area of Phu Phan Kham. There are deciduous forest and mixed forest growing on the rocky soil.

The weather in this area is three seasons. Summer is from March to May with hot temperature in April. Rainy season is from June to October with heavy rain in August. Winter is from November to February with very cold temperature in January because it has been influenced by high pressure from southern China.

The area generally has deciduous forest spreading all over especially on hillside and ridge. The valuable trees are Siamese sal, ingyin, eng, Kradone (a kind of Barringtoniaceae), Hiang and Payom (a kind of Dipterocarpaceae), and lower plants are wild cyad, slender bamboo, and many kinds of climber and prickly plants. In addition, there also has mixed forest in lower areas such as along the stream, in the valley, and on some of hillsides. The valuable trees are ironwood, Burmese ebony, Makhaa Tae, gyo, Krabog (a kind of Ixonanthaceae), and Teen nok (a kind of Verbenaceae), with bamboo is the lower plants. And the rain forest is growing only on the banks of stream. Its valuable trees are, for examples, Tabag (a kind of Lagerstroemia), Yang, Hopea, Makhaa mong, and rosewood.