Images of the crust and upper mantle obtained using teleseismic receiver functions exhibit a weak P-S conversion from the Moho in Western Argentina, where a segment of the subducting Nazca plate flattens out beneath the overriding South American plate. To better estimate depth to the Moho and search for mid-crustal impedance contrasts, we calculate high frequency receiver functions using 37 intermediate-depth local earthquakes. Radial receiver functions from a station located near San Juan, Argentina, show a strong signal from the Moho at 7 seconds corresponding to a depth near 50 km, and conversions from interfaces within the crust at depths of ~20 and 35 km. The higher frequency results obtained using local events have twice the vertical resolution of the teleseismic results and the combined data sets indicate a gradational increase in S velocity in the lower crust that cannot be detected in the lower frequency teleseismic data alone.