Harrowdale was the name given to the deep north-south valley cut out of the White Mountains by the Snowbourn River. At its southern end, beneath the mountain Starkhorn, stood Dunharrow, an ancient structure of the Men of the Mountains, later used as refuge of the Rohirrim. At its northern end, where the Snowbourn issued onto the plains of Rohan, stood Rohan's capital, Edoras.
It was in Harrowdale that the muster of Rohan took place before Théoden led his riders to Minas Tirith. At that time the Lord of Harrowdale was Dúnhere, who later died in the Battle of Pelennor Fields.