In northwestern Iceland, the Icelandic ice sheet began its non-uniform retreat about 15,000 years ago. Surface exposure dating using the isotope 36Cl was the primary means of dating boulders and terminal moraines in the Drangajökull area in Iceland. Ages of erratic boulders found near the Leirufjörður valley and moraine range from 7-12 thousand years old. The average ages for the groupings of boulders in the Leirufjörður area is 9.3 thousand years ago. Directly south of Leirufjörður in the Kaldalon Valley the average age of the boulders is 15,000 years old. The two different average ages are a result of different rates of glacial activity in Iceland.