Complex sentence: Mont Forel was once thought to be the highest mountain in the Arctic Circle area before the discovery of Gunnbjørnsfjeld in the Watkins Range over 350 km to the northeast.
Split into simpler sentences: Mont Forel was once thought to be the highest mountain in the Arctic Circle area. This was the higher Watkins Range, with the Gunnbjørnsfjeld, located over 350 km to the northeast.