Analysis of flood hazards for a 9-mile reach of Fortymile Wash and three of its tributaries was undertaken to aid in determining possible sites for the storage of radioactive wastes. Data from 12 peak-flow gaging stations adjacent to the Test Site were used to develop regression relations that permit an estimation of the magnitude of the 100-and 500-year flood peaks. The regional maximum flood was estimated on the basis of data from extreme floods elsewhere in Nevada and in surrounding states. On Fortymile Wash (drainage area at farthest downstreams cross section, 312 sq mi), the estimated maximum water depth for the three flood magnitudes are 8, 11, and 29 feet, respectively. Mean flow velocities would be as great as 9, 14, and 28 ft/s.