All the tests in '' Project 58 '' were one-point safety tests . They were intended to freeze device designs prior to full-scale tests at '' Operation Hardtack I '' . No significant yield was expected from either , but the second , '' Coulomb-C '' , a surface test conducted on December 9 , produced an unanticipated yield of 500 tons . Shortly after detonation , fallout readings of fifty roentgens per hour were recorded on the Mercury Highway , and , as the cloud moved toward the southwest , personnel at Jackass Flats involved in construction for future nuclear rocket testing were forced to take cover . Eventually , the cloud reached the Los Angeles area where readings caused public concern
Operation Hardtack I
Operation Hardtack I
Project 58/58A