Þjórsárdalur (]) is a valley in Árnessýsla county in Iceland that lies between mount Búrfell alongside the river Þjórsá to the east and mount Skriðufell to the west. The valley is quite flattened over and pumicey after repeated eruption of the nearby volcano Hekla as well as other volcanoes in the vicinity like the Vatnaöldur volcanic system which produced Iceland's biggest known lavafield Þjórsá Lava (Þjórsárhraun) in prehistoric times or the Grímsnes volcanic system with the crater Kerið. Landmarks in Þjórsárdal include Þjóðveldisbærinn Stöng, Gjáin, Háifoss, and Vegghamrar.