The simulation results indicate a thin sheet of high-vorticity fluid develops adjacent to the ground along the lee slope and then ascends abruptly as it is advected into the updraft at the leading edge of the first trapped lee wave. This vortex sheet is primarily forced by mechanical shear associated with frictional processes at the surface. Sub-rotor circulations develop along the leading edge of the parent rotor due to an instability of the vortex sheet, likely related to a type of Kelvin-Helmholtz instability. These sub-rotors are advected downstream or back toward the mountain within the parent rotor and occasionally intensify as exhibited by a several fold enhancement of horizontal vorticity. A preliminary vorticity budget indicates that horizontal vorticity generation due to the stretching of vorticity is 2-3 times larger than tilting and 5-10 times larger than baroclinic generation. The horizontal vorticity generation is enhanced near the edges of the wake emanating from the circular peak due to vortex stretching of the parent rotor and also further maximized due to stretching associated with three-dimensional turbulent eddies. The results suggest that preferred regions of intense sub-rotors may exist near topographic features that enhance vortex stretching.