Observation of the GZK Cutoff by the HiRes Experiment

We report on a decade of observation of the Ultra-high Energy Cosmic Ray spectrum by the HiRes experiment. We report on the observation of the GZK cutoff near the expected energy of 60 EeV. Associated dip structure in the spectrum near an energy of 5 EeV will also be discussed, and is consistent with electron-positron pair production energy loss mechanism for proton.