Moving from west to northwest, Mazama stratovolcanoes and shield volcanoes grow progressively younger. The oldest, at 400,000 years old, occur at Phantom Ship and Mount Scott, while the youngest can be found at the Hillman Peak stratovolcano, dated to 70,000 years old. There are also andesite flows at the northern rim of Mazama dated to between 50,000 and 40,000 years old. Shield volcanoes near Mazama feature lava flows made of agglutinated mafic andesite, which form sheets about thick, as well as more deposits from more viscous andesite and dacite magma that reach thicknesses up to . Many of these deposits (both dacitic and andesitic) contain undercooled, crystal-poor segments of andesite, including at Mount Scott and Phantom Cone. Lava and ice interactions are suggested by exposures of glassy breccia in Mazama's caldera, and lava flows cover glaciated lava deposits.