In 1959, 14 important forests were proposed for inclusion in national parks, among them the once vast and malarial Thung Salaeng Luang. Eventually, in 1972, 1,262 square kilometers were declared the Thung Salaeng Luang National Park.

But from the late 1960's to the early 1980's the forest was used as a major base area and infiltration route for guerrillas of the outlawed Communist Party of Thailand (CPT). It was sealed off by the Thai military from even the park officials. One of the climactic showdowns of the war with Communist insurgents took place at nearby Khao Kor, where government forces defeated the guerrillas in a series of tough battles in 1981 and 1982, Khao Kor is now the site of a resort and community-based development protects.

Guerrillas have not been the park's only scourge. Other intruders were hilltribe people and squatters who made use of the Phitsanulok-Lomsak highway running through the park's northern end to gain easy access to the area and stake claims to virgin terrian.

Composing the park are hills of limestone, slate and hardpan between altitudes of 300 to 1,028 meters. A long north-south stretch of limestone hills runs down the western section of the park. Thung Salaeng Luang, the origin of numerous streams, is inlaid with meadows, especially in its southern area. Mixed species deciduous forest predominates, with lowland scrub and tropical broadleaved evergreen covering smaller areas.

Nam Tok Kaeng Sopha

Dubbed the " Niagara Falls of Thailand," Kaeng Sopha is one of the country's most beautiful. The trees - tiered waterfall, shaped like a stairway, is found very hear kilometre 68 of the Phitsanulok - Lomsak Highway. Food stalls, rest rooms and a tourist nformation centre are located at the waterfall.

Three kilometres from the park office is an 80 metre long cable stayed bridge spanning the Khek Yai River. The riverbanks are pleasant for picnics and the Khek Yai is ideal for dips in the dry season although dangerous during the rains when the current flows too rapidly.

Thung Salaeng Luang

Thung Salaeng Luang : is reached by two routes. There is a 40 kilometre long trail running south from park headquarters to the meadow but it can only by negotiated by 4 - wheel drive vehicles and then only during the dry season. The other option is arriving via the Khao Kor - Phertchabun road which runs southeast of the park and turning off at Nong Mae Na. A gravel leads to the park boundary and meadow.