In today's Liangzhou, there are still two separatist forces: one is Han Sui in Jincheng County, and the other is Song Jian in Caohan.
Xiahou Yuan sent troops from Xingguo, quickly marched and besieged Caohan. After less than a month of fierce fighting, he succeeded in breaking Song Jian and beheading Song Jian and his set up prime ministers** (Taizu ordered Xiahou Yuan to lead the generals to crusade against Song Jian.
After Xiahou Yuan arrived in Caohan, he besieged the city, conquered it a month later, and beheaded Song Jian and the prime minister and others set up by him). Song Jian had ruled in Longxi County for more than thirty years, and although he had originally proclaimed himself King of Heshou Ping Han during the Liangzhou Rebellion, he remained neutral and did not participate in Ma Chao's rebellion.
Maybe that's why Xiahou Yuan didn't let him go. Because Song Jian's behavior of claiming the king made Cao Cao very dissatisfied, after all, Cao Cao was the prime minister of the Han Dynasty who "served the Son of Heaven to order not to be subordinate", and Song Jian actually called himself the king and claimed to be the king of Heshou Pinghan.
After Xiahou Yuan captured Caohan, he sent Zhang He to attack in the northwest direction and successfully captured Heguan County on the south bank of the Yellow River. Heguan County got its name because it was originally a pass built near the river, from which you can cross the Yellow River and enter the Hehuang Valley.