  The sharp change in slope of the ultra-high energy cosmic ray (UHECR)
spectrum around 10^{18.6} eV (the ankle), combined with evidence of a light but
extragalactic component near and below the ankle which evolves to intermediate
composition above, has proved exceedingly challenging to understand
theoretically. We show that for a range of source conditions,
photo-disintegration of ultra-high energy nuclei in the region surrounding a
UHECR accelerator naturally accounts for the observed spectrum and composition
of the entire extragalactic component, which dominates above about 10^{17.5}
eV. The mechanism has a clear signature in the spectrum and flavors of
neutrinos.
