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Four two-man teams and one five-man team supervised by the chief offsite monitor constituted the Offsite Monitoring Group. Before the detonation, the four two-man teams established monitoring posts in towns outside the test area. These towns were Nogal, Roswell, Fort Sumner, and Socorro, all in New Mexico. The five-man team remained at Guard Post 2 to assist in evacuation of nearby residences if the TRINITY cloud drifted in that direction. These residences, the Fite house and the homes in the town of Tokay, were 24 and 32 kilometers northwest of ground zero, respectively. Since the cloud drifted to the northeast, evacuation was not required. All offsite monitoring teams were in radio or telephone contact with personnel at the Base Camp (11).

Offsite monitoring teams in areas northeast of ground zero encountered gamma readings ranging from 1.5 to 15 R/h two to four hours after the detonation. Three hours after the detonation, surveys taken in Bingham, New Mexico (located 30 kilometers northeast of ground zero) found gamma intensities of about 1.5 R/h. Radiation readings at the town of White, nine kilometers southeast of Bingham, were 6.5 R/h three hours after the detonation and 2.5 R/h two hours later. Another team monitoring in a canyon 11 kilometers east of Bingham found a gamma intensity of about 15 R/h. Five hours later, the intensity had decreased to 3.8 R/h. It was estimated that peak intensities of gamma radiation from fallout on shot-day were about 7 R/h at an occupied ranch house in this canyon area (1; 11; 19).

Monitoring teams resurveyed these towns about one month after the TRINITY detonation. At Bingham, gamma readings of 0.003 R/h and 0.0001 R/h were found at ground level outdoors and at waist level inside a building, respectively. At the town of White, the highest outdoor gamma reading was 0.008 R/h. Inside a building, the highest reading was 0.0005 R/h (11).

Surveys taken in the canyon area one month after the detonation indicated that gamma intensities at ground level had decreased to 0.032 R/h. The occupied ranch house was also surveyed, both inside and outside. The highest reading outdoors was 0.028 R/h, and the highest reading indoors was 0.004 R/h (11; 19).

Monitoring was also conducted in offsite areas other than those to the north and northeast of ground zero. Monitors found no radiation readings above background levels (11).

Significant fallout from the TRINITY cloud did not reach the ground within about 20 kilometers northeast of ground zero. From this point, the fallout pattern extended out 160 kilometers and was 48 kilometers wide. Gamma intensities up to 15 R/h were measured in this region several hours after the detonation. One month later, intensities had declined to 0.032 R/h or less (11).