Densely spaced wide‐angle reflection data from oldest Archean crust in southern Minnesota were processed and modeled to place constraints on average crustal structure and the nature of the Moho. A preliminary 1‐D extremal inversion of τ(p) arrivals extracted from vibroseis and quarry blast recordings covering offsets betweeen 70 and 108 km suggests a crustal thickness between 45 and 51 km. Slowness‐depth models corresponding to extremal depths have average velocities ranging from 6.5 to 7.0 km/s, with velocities at the base of the crust ranging from 6.8 to 7.5 km/s. Estimates of Vp/Vs based on travel time ratios of P‐ and S‐wave arrivals show an increase from 1.71 ± 0.02 in the near‐surface to an average of 1.76 ± 0.03 for the whole crust, which is consistent with an increasingly mafic or plagioclase‐rich composition with depth. Although the data are sparse, the occurrence of broad‐band PmP, SmS, and PmS/SmP, arrivals at slightly precritical offsets combined with sporadic multicyclic reflections observed in coincident normal‐incidence CDP sections suggests that the Moho beneath this terrane is not a simple velocity gradient, but rather a layered zone involving small velocity contrasts. © 1993 by the Chinese Geophysical Society