Complex sentence: After surviving wounds he suffered in a battle with members of the Crow and Blackfoot tribes in 1809, he described a place of "fire and brimstone" that most people dismissed as delirium; the supposedly imaginary place was nicknamed "Colter's Hell".
Split into simpler sentences: After surviving wounds he suffered in a battle with members of the Crow and Blackfoot tribes in 1809, he gave a description of a place of "fire and brimstone" that was dismissed by most people as delirium. The supposedly imaginary place was nicknamed "Colter's Hell".