ongs an ▁waters hed ▁covers ▁roughly ▁ 1 , 1 6 7   km ² ▁( Jo ▁ 1 9 8 7 : 3 5 ). ▁ ▁The ▁H ye ongs an ▁flows ▁north ▁from ▁near ▁the ▁northern ▁border ▁of ▁Gre ater ▁U ls an ▁into ▁G ye ong ju ▁city , ▁where ▁it ▁enters ▁the ▁G ye ong ju ▁Bas in ▁and ▁is ▁joined ▁by ▁the ▁B uk che on ▁stream ▁( 북 천 /), ▁a ▁major ▁trib ut ary . ▁ ▁It ▁continues ▁north ▁into ▁P oh ang ▁city , ▁and ▁in ▁Ang ang - e up ▁of ▁P oh ang ▁it ▁is ▁joined ▁by ▁the ▁G ig ye che on ▁flow ing ▁from ▁the ▁north ▁and ▁turns ▁ab rupt ly ▁east ward . ▁ ▁From ▁there ▁runs ▁east ▁and ▁slightly ▁north ▁until ▁it ▁meets ▁the ▁Sea ▁of ▁Korea ▁at ▁P oh ang ▁Har bor . ▁ ▁The ▁est u ary ▁of ▁the ▁H ye ongs an ▁has ▁been ▁covered ▁by ▁the ▁massive ▁industrial ▁development ▁around ▁the ▁port ▁of ▁P oh ang , ▁including ▁the ▁P OS CO ▁steel ▁mill . ▁ ▁History ▁The ▁H ye ongs an ▁is ▁primarily ▁notable ▁for ▁the ▁S illa ▁civil ization ▁which ▁arose ▁within ▁its ▁valley , ▁centered ▁at ▁G ye ong ju . ▁ ▁Middle ▁Je ul mun ▁Pot tery ▁Period ▁pot sh erd s ▁have ▁been ▁un ear th ed ▁in ▁the ▁H ye ongs an ▁Bas in . ▁Several ▁significant ▁M um un ▁settlement s ▁arose ▁along ▁the ▁river ▁after ▁ 1