The approximate physical distribution and condition of displaced and ruptured rock materials in the Rainier and Neptune areas were established by geologic observation of structural and lithologic details, and stratigraphic correlations. The effects of the detonations were found to be related to the rock types considered from the standpoint of engineering materials as well as to their structural positioning. Gross displacements and fracturing are in apparent accord with Mohr theory of rupture stress orientation. Factual data find explanation on the fundamental basis of primary (blast) and secondary (gravity) induced principal stresses. The 90 plus or minus 20-ton Neptune explosion disaggregated and displaced rock materials to a radial distance which ranged between 45 and 100 feet from ground zero depending on the orientation of bedding plane weaknesses and proximity of the ground surface to the point of detonation. Primary fracturing extended from ground zero to a radial distance which ranged from 55 feet to an estimated 145 feet depending on the favorable distribution of geologic structural weaknesses. Neptune was found to exhibit primary (blast) and secondary (gravity) rupture features which are fundamentally the same as those found in thc Rainier area. The 1700-ton Rainier shot initiallyformed a fused- rock-lined cavity ofmore » an average 62 plus or minus 10foot radius below ground zero and an undetermined radius above ground zero Gross primary rock displacement and gain disaggregation took place to a radiul distance of from 80 to 130 feet from ground zero. Visible primary fracturing extended to a radial distance which ranges between 150 and 220 feet depending on the proximity of hard brittle rock (welded tuff) which, it is concluded, transmitted rupture stresses to a much greater distance than the "punky" granular tuff. Collapse of rock material into the initial cavity was favored by primary shear fractures, which developed prominently to a radius of 150 feet from ground zero. The collapsed rock defines a 100-foot-diameter cylindrical zone. This zone is presumed to extend for 388 feet upward from ground zero. A dome-shaped top is postulated on the basis of Mohr stress theory. It should be noted that, with the exception of drill hole G, there has been no drilling or underground working above the Raise'' Drift. Cavities, distributed around the perimeter of the cylinder, are attributed to variations in the coherence of the rock strata which were disrupted during collapse. The collapse block has remained essentially intact. This fact, coupled with the virtual absence of radioactive fission products above ground zero and nearly complete pulverization of the central collapse block, leads to the conclusion that underground nuclear explosions are applicable to mining by block-caving methods. Furthermore, material within the crushed zone should be mineable without the use of additional explosives. The mineability of material within the fracture limit is a question that is difficult to answer at present, as the degree of fracturing has not been established. Perhaps the direct approach of experimental excavation would be the best solution to the problem. The conclusions presented should be considered as hypotheses awaiting verification. There is still much to be learned from the Rainier explosion. (auth)« less