We use scanning near-field optical microscopy and spectroscopy to investigate the near field of one-dimensional periodic arrays of gold nanowires on top of a slab waveguide. The Bragg resonance of these one-dimensional metallic photonic crystal slabs can coincide with the particle-plasmon resonance of the metal nanowires, giving rise to an avoided crossing. We find a rich behavior when systematically varying the polarization of the incident light, the lattice constant, and the slab thickness. Numerical simulations of the transverse magnetic component of the near field qualitatively reproduce the experiment, in agreement with the expectation from the Bethe-Bouwkamp theory. Furthermore, these calculations give insight into those electromagnetic field components which cannot easily be measured.