  We report a transition from a disordered state to an ordered state in the
flow of nearly mono-disperse granular matter flowing in an inclined channel
with a bumpy base, in discrete element method simulations. For low
particle-sidewall friction coefficients, the particles are disordered and the
Bagnold velocity profile is obtained. However, for high sidewall friction, an
ordered state is obtained, characterized by a layering of the particles and
hexagonal packing of the particles in each layer. The extent of ordering,
quantified by the local bond-orientational order parameter, varies in the
cross- section of the channel, with the highest ordering near the side walls.
The flow transition significantly affects the local rheology: the effective
friction coefficient is lower, and the packing fraction is higher, in the
ordered state compared to the disordered state. A simple model, incorporating
the extent of local ordering, is shown to describe the rheology of the system.
