  We have measured the spectrum of UHE cosmic rays using the Flash ADC (FADC)
detector (called HiRes-II) of the High Resolution Fly's Eye experiment running
in monocular mode. We describe in detail the data analysis, development of the
Monte Carlo simulation program, and results. We also describe the results of
the HiRes-I detector. We present our measured spectra and compare them with a
model incorporating galactic and extragalactic cosmic rays. Our combined
spectra provide strong evidence for the existence of the spectral feature known
as the ``ankle.''
