The origins of the Jeulmun are not well known, but raised-clay pattern Yunggimun pottery (융기문토기; 隆起文土器) appears at southern sites such as Gosan-ni in Jeju Province and Ubong-ni on the seacoast in Ulsan.
[5] Choe and Bale estimate that at least 14 Middle Jeulmun period (c. 3500-2000 BC) sites have yielded evidence of cultivation in the form of carbonized plant remains and agricultural stone tools.
[13][14] However, not all archaeologists accept the grains as domesticated millet because it was gathered out of context in an unsystematic way, only black-and-white photos of the find exist, and the original description is in Korean only.
Lee suggests that environmental stress on shellfish populations and the movement of people into the interior prompted groups to become more reliant on cultivated plants in their diets.
Archaeologists have suggested that Bangudae and Cheonjeon-ri, a substantial group of petroglyph panels in Ulsan, may date to this sub-period, but this is the subject of some debate.
Kim Jangsuk suggests that the hunter-gatherer-cultivators of the Late Jeulmun were gradually displaced from their "resource patches" by a new group with superior slash-and-burn cultivation technology and who migrated south with Mumun or undecorated pottery (무문토기; 無文土器).