The results of temaperature measuring experiments conducted for Rainier shot, Operation Plumbbob are described, The temperature distribution in the surrounding tuff resulting from the detonation of an underground nuclear device yielding 1.7 kilotons of energy has been measured, Data indicate peak temperatures in the vicinity or 90 deg existing in the central regions which drop rapidly to approach ambient temperatures at distances of about l80 feet from the original ground zero, Based on measurements taken in three holes drilled into the central regions, contours of constant temperature are constructed The temperature picture is consistent with the consideration that most of the heat entered the water contained originally in the tuff and the unconsolidated material which filled the cavity after its initial collapse, The amount of energy contained in the central regions in the form of tuff heated to below 90 deg C is roughly estimated to be greater than one-half of the total energy release. An unsuccessful attempt to measure the temperature rise across the shock front of the pressure wave produced by the detonation is described, and reasons for failure are discussed. (auth) A slow chopper neutron velocity spectrometer was used to measure the energy spectrum of thermal neutrons …