The three glacial Malrif lakes (Grand Laus, Petit Laus, and Mézan) are located between 8,461 and 9,202 ft (2,579 and 2,805 m) above sea level in an environment mainly composed of lustrous shale from the Piedmont area of the Queyras Massif. These rocks testify to the presence, 150 million years ago, of the 9,842 ft (3,000 m) deep Ligurian Tethys ocean. The lustrous shales formed from the non-pure clayey limestone sediments deposited at the bottom of this ocean. These sediments have undergone several metamorphisms and retro-metamorphisms that have given them a shiny patina.