Fjaðrárgljúfur is a magnificent and massive canyon, about 100 meters deep and about two kilometres long. The canyon has sheer walls, and is somewhat serpentine and narrow. The bedrock in Fjaðrárgljúfur is mostly palagonite from cold periods of the Ice Age and is thought to be about two million years old. The river Fjaðrá has its source in the mountain Geirlandshraun and falls off the heath edge in this stunning canyon until it makes it down into Skaftá river.