  Extreme Energy Cosmic Rays, EECRs -- cosmic rays with energies beyond the GZK
cutoff (i.e. greater than 100 EeV) are scarce. Only a few of such events have
been detected by air shower experiments and the nature of the primary particles
are still unknown. Individual EECRs sources become more prominent, relative to
the background, as the horizon diminishes. We show that an event-by-event,
composition-dependent observatory would allow us to limit the character of the
sources and learn about the intervening magnetic fields, as the deflections in
the intervening Galactic and extragalactic magnetic fields depend on the nature
of the particle. A major goal here is to provide a methodology to distinguish
between steady and transient sources.
