  Physics beyond the standard model might imply the cosmological production of
particles with grand unification scale energies. Nucleons and gamma-rays from
such processes are candidates for the cosmic rays observed beyond 100 EeV
[10**(20) eV]. Using a new particle propagation code, we calculate the neutrino
fluxes predicted by such scenarios if consistency with the observed cosmic ray
flux and the universal gamma-ray background at 1-10 GeV is required. Flux
levels detectable by proposed km**3 scale neutrino observatories are allowed by
these constraints. Bounds on or detection of a neutrino flux above about 1 EeV
would allow neutrino astronomy to probe grand unification scale physics.
