A Handful of Dust

From the PDF:

Deserts preserve secrets, and the dusty wastelands of New Mexico have buried many. Nearby the test site of the world's first atomic bomb, a centuries-old coven of witches has been resurrected, and Delta Green has been alerted to the emerging threat. Dispatched to the scene, the investigating agents are yet to learn that a far older radioactive horror may overshadow all their expectations.