Granite plutons within Grand Canyon's Precambrian crystalline basement were likely created supernaturally on Creation Days 1–2. They were then uplifted by the upheaval on Creation Day 3. These granites were not generated during the Flood because at the onset of the Flood they were already in place within the schists and were beveled before Flood sediment layers were deposited unconformably over them. Sixty-eight samples were collected from ten granite plutons and two pegmatite complexes. Radiohalos in these samples were identified and counted, only 27 (~40%) contain 238U radiohalos, compared to 46 (~68%) which contain 210Po radiohalos and 22 (~32%) which contain no radiohalos. Two models proposed previously to resolve the Po radiohalos enigma are creation by fiat of the host granites with their Po radiohalos during Creation Days 1–2, or rapid transport of the Po atoms by hydrothermal fluids expelled from rapidly crystallizing granite magmas while grossly accelerated radioactive decay was occurring during the Flood. Since these are supernaturally created granite plutons any radiohalos in them likely were annealed by the Creation Day 3 upheaval and the onset of the Flood. Thus, the origin of these radiohalos is consistent only with the hydrothermal fluid transport model for their formation during the Flood. Water trapped in the Flood-deposited sediment layers was heated by their burial and the residual heat generated by grossly accelerated radioactive decay. The favored model is that these hydrothermal fluids circulated into the underlying basement granites where they transported Po atoms generated by grossly accelerated decay of 238U within zircon crystals inside the granites' biotite flakes. Some of these Po atoms were scavenged from solution at defect sites along cleavage planes within the biotite flakes and produced Po radiohalos, many without adjacent 238U radiohalos. Compared with a similar process that occurred in granite magmas that crystallized and cooled also during the Flood, this process in already solid Creation Week granites was a slower, less effective process that likely lasted for months. The 210Po atoms being longer-lived than 218Po and 214Po atoms were transported further by these hydrothermal fluids of lesser volume and less vigorous circulation than hydrothermal fluids expelled from granite magmas that were generated and crystallized during the Flood.