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We present new results on the crustal and upper mantle structure beneath the rift mountains along two segments of the Mid‐Atlantic Ridge and across a nontransform offset (NTO). Our results were obtained from a combination of forward modeling and two‐dimensional tomographic inversion of wide‐angle seismic refraction data and gravity modeling. The study area includes two segments: OH‐1 between the Oceanographer fracture zone and the NTO‐1 at 34°35′N and OH‐2 between NTO‐1 and the NTO at 34°10′N. The center of OH‐1 is characterized by anomalously thick crust (∼8 km) with a thick Moho transition zone with V_p = 7.2–7.6 km/s. This transition zone, coincident with a gravity low, is probably composed of gabbro sills alternating with dunites, as observed in some ophiolites. OH‐1 has larger along‐axis crustal thickness variations than OH‐2, but average crustal thicknesses are similar (6.0±1.2 km at …