The growth and resulting crystallography of Cu nanowire arrays fabricated using glancing angle deposition are studied. On native oxide Si(100), the nanowires exhibited a strong (110) texture for a deposition angle θ=75° with rotational symmetry of the low energy Cu about the long axis. On hydrogen-terminated Si(110), the wires are epitaxial with the substrate. The critical height for epitaxial growth is maximal at θ=35°, and decreases rapidly with increasing deposition angle. Based on the growth mechanisms in glancing-angle-deposited materials, the theory of growth mode in epitaxial thin films, and the observations about texture formation in epitaxial and nonepitaxial Cu nanowires; we discuss the observed growth modes in epitaxial nanowire arrays.