1. INTRODUCTION The considerable work on the mechanism of formation and properties of fallout has used data from Pacific Ocean events (coral island or sea water emplacement) and from excavation exper iments (Fr70, K164). However, about 90% of the Nevada and Utah population's exposure to radioactive fallout from nuclear weapons testing in Nevada during the years 1951 through 1957 was due to 16 devices (An81) detonated on steel towers 300-700 feet above the ground. No data from shots emplaced on steel towers at the Nevada Test Site have been compared to the accepted model because the only data extant were taken for another reason, i.e., to study the uptake of radionuclides by animals living in the fallout pattern (La66). Only some of the data were reported, thus preventing their use in checking the fallout model or these calculations. The Nevada Operations Office of the U.S. Department of Energy has recently acquired the laboratory notebooks containing more of the data. This work describes the comparison of all these data with results derived from the fallout composition model. In this work I have developed a method to calculate the ground concentration (uCi/m?) of each radionuclide from the external gamma exposure rate given by the fallout pattern. fractionation are included. The effects of The results are compared with field data and interpreted according to the accepted model of fallout formation (Ad60). The calculations agree in detail with the field data; thus, the fractionation behavior of offsite fallout from tower shots within 160 miles of ground zero is well characterized. Uranium and plutonium