The High Resolution Fly's Eye (HiRes) was a
Cherenkov detector to detect cosmic-ray
operating in western Utah from 1997 to 2006.
It was a follow-on to the Fly's Eye and precursor
to the current Telescope Array Project (TA).
Compared to the Fly's Eye, which watched the whole sky for
air showers, HiRes concentrated on a portion of the sky
but with smaller pixels providing better angular resolution.
An initial configuration (HiRes-I) used a ring of 22 telescopes
covering elevations from 3° to 17°.
An additional configuration (HiRes-II) was later added some
distance away, covering elevations from 3° to 31°.
Underground muon detectors collected additional data regarding
the aftermath of the air showers.