The group already found out the remains, which witness salt production by Koguryo circa the 4th century, in the area of Wonup, Onchon County, Nampho City in 2013 through steady excavation from early Juche 101 (2012).

The newly-unearthed remains were found on mounds in a paddy field of the Wonup Co-op Farm, which is about 3 kilometers northeast of the seat of Wonup Workers' District.

The group discovered stone installations in five sites and proved in a scientific way that one of them belongs to the period of Josonhuguk.

The stone installation of Josonhuguk was buried 120cm deep under the ground surface and shapes a ring with thick ash layer inside it. According to experts, the ring is 145cm and 240cm in its interior and exterior diameters respectively and has a trace of fire hole in the south, so that it can be considered to be a big oven.

Pieces of light gray and brown earthenware and iron pieces including two pocket-type axes were gathered from around the stone installation. The earthenware pieces are the same as those left by ruined people of Kojoson (early 30th century B.C.-108 B.C.). And especially, pieces of light gray earthenware representative of hard potteries made in Josonhuguk have much in common with those unearthed in brick tombs dating back to the 2nd century-3rd century. The axes are also relics which came to be used since about the 2nd century.

Therefore, it is clear that the date of the newly-unearthed remains can be set at the 1st century-2nd century and the area of Onchon was under the control of Josonhuguk in the period.

Through the study of the remains, it was brought to light that salt was produced by evaporating seawater with the use of plants or ashes and boiling it.