We have used cathodoluminescence spectroscopy with variable incident beam energies to study the energy levels and activation of Er impurities in GaN as a function of depth below the free surface. The GaN films were doped in situ during either metalorganic molecular-beam epitaxy (MOMBE) or molecular-beam epitaxy (MBE). Besides the well-known Er3+ luminescence at 0.80 eV, we observe emissions at 1.2, 1.8, 2.2, and 2.3 eV, corresponding to higher energy Er 4f shell transitions. For unannealed MOMBE-grown GaN:Er, these higher energy emissions appear only for excitation depths of hundreds of nanometers. The MOMBE-grown GaN;Er annealed to 500 degrees C shows a dramatic increase in the 1.8, 2.2, and 2.3 eV peak intensities at shallow probe depths, with its yield increasing with increasing depth. These three features become pronounced at all depths after a 700 degrees C anneal, MBE-grown GaN:Er grown with lower C and O impurity levels than the MOMBE-grown sample exhibits strong emission at all these energies without annealing. The decreased emission at shallow (tens of nanometer) probe depths suggests a depletion of activation Er in the near-surface region. Enhancement of near-surface Er3+ luminescence with annealing may be due to lattice reordering as well as impurity redistribution.