The Drumroot was a cave system used by the Utaru of Riverhymn as a safe haven for those village members who were unable to fight. However, since the Derangement, machines patrolled inside, making it perilous. The waterfalls inside the Drumroot served as the water source for the village.
When Regalla's Rebels threatened Riverhymn, the metalweaver Kue sent one of his hunters, Vaus, to reach the top of the Drumroot to harvest fertilizer pods produced by the Widemaws that grazed above it, so that Kue could make weapons for the fight ahead. When Vaus did not return, Kue sent the huntress Aloy after him. She discovered that Vaus had been killed by Burrowers inside the cave system, which Aloy killed in turn and retrieved Vaus's seed pouch. She continued up the Drumroot, collected the fertilizer pods and returned to Kue.