  We have investigated the magnetoresistance of lithographically prepared
single-layer graphene nanoribbons in pulsed, perpendicular magnetic fields up
to 60 T and performed corresponding transport simulations using a tight-binding
model and several types of disorder. In experiment, at high carrier densities
we observe Shubnikov-de Haas oscillations and the quantum Hall effect, while at
low densities the oscillations disappear and an initially negative
magnetoresistance becomes strongly positive at high magnetic fields. The strong
resistance increase at very high fields and low carrier densities is
tentatively ascribed to a field-induced insulating state in the bulk graphene
leads. Comparing numerical results and experiment, we demonstrate that at least
edge disorder and bulk short-range impurities are important in our samples.
