Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 131. Looming up as a dark ridgeline on the western plain, paha sapa, the Black Hills of South Dakota and Wyoming are a jewel of America, treasured by the Native American, the white explorer, the frontiersman, the cowboy, the gold prospector, the miner, the camp follower, the settler, the businessman, the tourist and also the geologist. History, folklore and legend are as conspicuous as outcrops for the geologist who travels the Black Hills. The Black Hills is a microcosm of geology.