  We present a model-independent analysis of the mass spectrum of nonstrange
l=1 baryons in large N_c QCD. The 1/N_c expansion is used to select and order a
basis of effective operators that spans the nine observables (seven masses and
two mixing angles). Comparison to the data provides support for the validity of
the 1/N_c expansion, but also reveals that only a few nontrivial operators are
strongly preferred. We show that our results have a consistent interpretation
in a constituent quark model with pseudoscalar meson exchange interactions.
