Seismic refraction data collected by using a large air gun source and ocean bottom hydrophone receivers show that within two areas on the flanks of the East Pacific Rise the structure of the uppermost 2 km of the crust is laterally homogeneous. The two areas are 20 and 40 km in extent on 0.5 and 4 m.y. old crust, respectively, and are separated laterally by 110 km. A small but significant difference in structure exists between the two areas, the younger crust exhibiting the higher velocities. Ray tracing through laterally heterogenous models of the shallow crust, the careful calculation of corrections for seafloor topography, and the objective comparison of data sets by using the slant stacking approach suggest that the established apparent variability in shallow crustal structure may in part be an artifact of experimental and interpretative techniques. We propose a reasonable model for shallow crustal structure in which the isovelocity contours parallel the seafloor topography: this permits determination of lateral homogeneity of the velocity gradient in the shallow crust over the subdued topography of the East Pacific Rise, or in the deeper crust in general, where vertical velocity gradients are sufficiently small that topography has negligible effect on the velocity field.