Wiang Kosai is the first national park in Prae Province. It covers Long District and Wang Chin District, Prae Province and Tern District, Sobprab District and Mae Ta District, Lampang Province. There are crossed over by high steep mountains and many beautiful waterfalls, e.g. Mae Koeng Luang, Mae Koeng Noi, and also Mae Jork Hot Spring which is the source of rivers and streams. The area of the park is about 410 Km2 (256,250 Rai).
The landscape is high steep mountains, the average steep is 80 degree. The highest point from sea level equals 1,267 meters whereas the average equal 800 meters. Covering with evergreen forest and mixed deciduous forests and overlapping high steep cliffs that are the sources of many streams e.g. Mae Koeng, Mae Jork, Mae Sin and Mae Pak. Since mountain is sandstone, it makes the soil decayed from the mountain become sandy soil with fine ventilation. The plain area nearby the slopes of the hill is good condition laterite soil.
Summer, March to May, the maximum temperature is around 39°C in April. From June to October is the rainy season and during the winter, November to February, The minimum temperature is around 13°C in December.
Flora and Fauna
In the upper side of the mountain range covers with dry evergreen forests whereas the lower side are mixed deciduous forests. The important plants are Oramosia, rubbers, genus diospyros, Lagerstroemia, red pterocarpus and teaks, and also the forest floor e.g., bamboo, palms, rattans, dendrobium, etc.
The forests are the living place of various kinds of wild animals e.g. tiger, elephant and deer. But a large number of the animals were hunted illegally. Nowadays there are only small animals to see such as barking deer, wild boars, squirrels, chipmunks and several kinds of birds that are plentifully lives in the valleys and river sources.