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 &tgr;(p) arrivals extracted from vibroseis and quarry blast recordings covering offsets between 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. ¿ American Geophysical Union 1993