With energies greater than a PeV, cosmic rays from galactic (and extra-galactic) sources are too rare to detect directly.  Instead, large ground-based detector arrays catch the secondary particles from the extensive air showers produced in the atmosphere, and attempt to determine indirectly the underlying spectrum and mass composition.  The IceCube Observatory has a surface detector called IceTop, which can help to answer these questions... questions which are linked to the mystery of these particles' origin.