This study examines the transition from fluid behavior to solid behavior that too often occurs in granular flow and brings with it such unwelcome events as funnel flows in hoppers and other clogging of material handling devices. This situation is studied using a discrete particle computer simulation of a Couette flow with gravity. This simulation exhibits the full range of granular flow behavior, from a stagnant solid-like material, through a quasistatic transition zone, to a rapid granular flow. The most important result is that the first motion in the material just above the static bed, occurs in a quasistatic mode at a fixed value of the stress ratio rxy/ryy. Thus it appears that the location of the transition from solid to fluid behavior can indeed be described by a Mohr-Coulomb failure criterion.