"On a research trip, I was traveling with several Indians on horseback across the rolling plains of Montana," says Howard Terpning. "Suddenly, a wind came up and the sky turned an ominous blue black. A white cloud developed and moved across the horizon from left to right, billowing into a formation that seemed to grow up from the ground amid loud claps of thunder. I know that the incident had to be recorded, and Thunder Speaks is the result."