The site structure beneath the five broadband stations of the Regional Seismic Test Network (RSTN) has been determined utilizing teleseismic P waveforms. Our teleseismic waveform modeling technique involves inverting the radial component of stacked source-equalized receiver functions in the time domain to estimate the vertical shear velocity structure at the site. The receiver functions at RSNY (Adirondacks, New York), RSON (Red Lake, Ontario), and RSNT (Yellowknife, Northwest Territory) are quite simple compared to previously published RSCP (Cumberland Plateau, Tennessee) data, largely due to the absence of sedimentary surface rocks at these sites. At RSNY, a high-velocity layer at mid-crustal depths (18 to 26 km) in our southeast backazimuth results correlates in depth with a zone of high-amplitude reflections found on COCORP profiles 60 km south of RSNY. A gradational crust-mantle boundary is observed at RSCP and RSNY. The RSON and RSNT sites are characterized by simple crusts with fairly abrupt crust-mantle boundaries. The crust beneath RSON appears to have a clear division between the upper and lower crust at about 18 km depth while this boundary is not well-developed at RSNT. Pronounced azimuthal variations in crustal structure at RSSD (Black Hills, South Dakota) prohibit the determination of velocity using a layered earth model. The crustal thicknesses at each of these sites are: RSCP, 40 to 50 km; RSSD, 47 to 50 km; RSNY, 45 to 50 km; RSNT, 38 km; and RSON, 42 km.