Gloppedalsura consists of avalanche boulders that are piled on top of an end moraine. 10,000 years ago the ice sheet that covered the area, melted away. For a period of time the massive end moraine dammed the Hunnedal river's former course, towards Veen and Vikeså, and formed a lake in Byrkjedalsgryta. The terraces in Byrkjedal at 240 metres altitude are evidence of this moraine-dammed lake. The annual cycle of frost and expanding ice broke free a vast number of boulders and rocks and sent them tumbling down the southern mountainside. This debris settled as a 100-metre thick scree on top of the moraine.