Laser-based photoemission sources provide the unique opportunity to study dynamic electronic processes at surfaces and interfaces. Using angle-resolved, laser photoemission with < 1 ps time resolution, we have directly observed a new surface band at the X̄ point in the GaAs(110) surface Brillouin zone. The appearance of electron population in this valley occurs only as a result of scattering from the directly photoexcited valley at Г. The momentum resolution of our experiment has permitted us to isolate the dynamic electron population changes at both Г and X̄ and to deduce the scattering time between the two valleys.