The volcano is about 1.45 ± 0.41 million years old, and Llullaillaco I is of early Pleistocene age. The oldest date, 1.5 ± 0.4 million years ago, was determined on a lava flow northwest of Llullaillaco's main edifice. Two dates obtained on lava flows of Llullaillaco II are 401,000 ± 6,000 and 1,500,000 ± 400,000 years ago, based on argon-argon dating and potassium-argon dating respectively. The northern young lava flow is less than one million years old based on potassium-argon dating, the southern flow is 48,000 ± 12,000 years old based on argon-argon dating on biotite. Surface exposure dating based on helium has yielded ages of 41,000 ± 1,000 years for Llullaillaco I at over altitude and of 5,600 ± 250 years for Llullaillaco II at an altitude of over .