Experimental studies of the reflection, transmission, and absorption of high-power microwave pulses from a plasma-covered plane conducting boundary are presented. Under optimum conditions, backscattered rf power is attenuated by more than 30 dB over values measured in the absence of the plasma. Measurements of the radial and axial plasma density profiles and the neutral gas pressure near the plane conductor indicate that collisional absorption processes are not the primary source of the observed attenuation in the backscattered microwave signal, and that the plasma density exceeds the critical density over much of the volume nearest the conductor. The effects of a tenfold reduction in the microwave power density on the reflection and absorption characteristics of the system are also reported.