Strong motion observations within the mesa adjacent to Rainier shot of Operation Plumbbob (1.7 kt) were made on a horizonal radius (long the access tunnel) and a vertical radius by Sandia Corporation under Project 26.4b. Principal data were derived from radial component acceleration measurements. Long-base strain gages provided some secondary data. Horizontal radius data were derived from gages at distances ranging from 100 to 1,355 feet from the burst point. Vertical radius data were obtained over distances ranging from 366 to 896 feet at the mesa top surface. Many of the accelerometers used in Project 26.4b were given set corder system overloading caused saturation and serious loss of precision in record peak amplitudes. All arrival time data are good, but ampitude data are questionable in many cases. Accelerometers at closer stations on both radii were not seriously overranged and data from them are reliable. Corrections based on a few records from Project 26.4a gages of a vertical radius installation were made for thc overranged Project 26.4b gages of the vertic:ofl r~ddius. Corrcetcyl ofdnd radius installation were made for the overranged Project 26.4b gages of the vertical radius. Corrected and uncorrected acceleration-time data for the vertical radius gages were converted tomore » particle velocity and displacement information by integration. Horizontal radius data show peak accelerations dccreasing approximately as the inverse fourth power of radial range between about 3,500 g at 100 feet and 10 g at, roughly, 400 feet where the rate of decrease approaches the inverse square of range. Peak accelerations from the vertical radius decrease with range up to thc vicinity of transition from weak bedded tuff to the welded tuff (rhyolite) cap rock. From this region upward toward the surface record, charactcr changes radically. A sharp upward acceleration pulse is followed by a relatively long period of free fall at about -- 1 g (true zero g for the accclerometer biased to +1 g in calibration). A sharp upward robound pulse and a decaying oscillatory train complete the motion. Free fall originates at all gages nearly simultaneously but ends at progressively later times upward. Rebound initiation sequence suggests that horizontal parting or spalling occurred at three levels from beneath the cap rock upward to the surface. Initial peak accelerations through the cap rock region increase with increasing radial range. This cannot be attributed to surface reflection except at the surface gage. The anomalous incrcase in amplitude may be caused by continuously decreasing seismic impedance (pc) upward through the cap rock, with consequent continuous refletion of the compression wave with enhanced peaks. Horizontal strain gages on the tunnel walls survived for periods too short to observe significant motion. Strain gages on the vertical radius showed significant, but small, compressive strains; however, they may have been constrained from free tensile motions by mounting cables. (auth)« less