A wide-angle reflection-refraction experiment, sponsored by the Program for Array Seismic Studies of the Continental Lithosphere (PASSCAL), was conducted in the Ouachita Mountains area of southwestern Arkansas and northwestern Louisiana. This experiment employed 400 state-of-the-art seismic recorders and overlapped the southern one-third of the COCORP (Consortium for Continental Reflection Profiling) deep seismic reflection profile in the area. A wide variety of data processing and interpretation techniques was employed to derive an Earth model from these data. The model depicts a preserved early Paleozoic continental margin buried beneath allochthonous Paleozoic strata and younger sedimentary rocks. The southern part of the model indicates the presence of oceanic or highly extended continental crust overlain by about 15 km of mostly Paleozoic sedimentary rock. These results are consistent with little if any shortening of crystalline continental crust during the Ouachita orogeny.