  The High Altitude Water Cherenkov (HAWC) Observatory is a wide-field-of-view
gamma-ray observatory that is optimized to detect gamma rays between ~300 GeV
and several hundred TeV. The HAWC Collaboration recently released their third
source catalog (3HWC), which contains 65 sources. One of these sources, the
ultra-high-energy gamma-ray source 3HWC J1908+063, may exhibit a hardening of
the spectral index at the highest energies (above 56 TeV). At least two
populations of particles are needed to satisfactorily explain the highest
energy emission. This second component could be leptonic or hadronic in origin.
If it is hadronic in origin, it would imply the presence of protons with
energies up to $\sim$1 PeV near the source. We have searched other 3HWC sources
for the presence of this spectral hardening feature. If observed, this would
imply that the sources could make good PeVatron candidates.
