GURPS Technomancer, softback supplement for GURPS, by David L. Pulver
“On July 16, 1945, the first atomic bomb was detonated at Trinity Site in New Mexico. The explosion ripped a hole in the fabric of space. Doctor Oppenheimer’s words “I am become death, destroyer of worlds” unwittingly closed a necromantic ritual. The fireball vanished, but the mushroom cloud remained. This was the Hellstorm, a tornado of seething magical energy.
A pattern of enchanted fallout drifted across the southern United States and Mexico. The effects would not be felt immediately, but over the next generation, they would transform the world…
Magic had come to the modern 20th century. But like the power of the atom on our own Earth, it would prove a Pandora’s Box.”