The highest-energy cosmic rays
  This paper begins with a pedagogical discussion of the propagation of cosmic rays and the showers produced when a cosmic ray primary hits the upper atmosphere. The paper focusses cosmic rays, with energy > 10^19 eV. Emphasis is placed on the shower properties that are relevant to the detection of cosmic rays by surface arrays and fluorescence telescopes. The two major experiments, AGASA and HiRes are described in some detail. Then the experimental results are reviewed. It is no surprise that more data will be needed. But it is also true that improved analysis and further data from HiRes can make significant improvements in the experimental situation. 
James W. Cronin