The Ytri-Rangá is a lowland spring-fed river — geomorphologically very unusual. It rises at Rangárbotnar, about 200 m above sea level on the lava fields north of Hekla, where water emerges in multiple springs from beneath porous postglacial basalt flows and stays stubbornly clear because the lava aquifer filters the runoff. Over its 55 km the river runs through volcanic-sand and basalt-cobble substrate, the bed reworked by mobile dark sand that gives it a distinctly non-alluvial character: this is not a gravel-bed pool-riffle reach but a broadly sinuous channel (the name Rangá literally means winding river) with shallower, more uniform runs, punctuated by four named bedrock steps — Fossabrekkur, Gutlfoss, Árbæjarfoss and Ægissíðufoss. The Þverá joins roughly 10 km below Hella and the combined water becomes the Hólsá. Wading is broadly easy on firm cobble, but loose volcanic sand near inside bends can engulf a boot unexpectedly.

Wading: Loose volcanic sand on inside bends