The gold mining activity in Dakota is comprised within the Black Hills and occupies a metamorphic range covering an area of 900 sq miles, extending north and south through the central portions of the hills. The old miners for convenience in making laws to govern the recording and locating of claims divided the gold fields into different districts based on the value and character of the gold deposits. The gold obtained from gravels on French Creek was in small flattened scales and grains, quite uniform in size, mixed with very little fine dust, and nearly free from magnetic iron sand. It showed little action of water, and the garnet crystals associated with it were often quite perfect and scarcely rounded by attrition. The greater portion of the gold was derived from the quartz ledges in the schistose rocks. The exploration and prospection in French Creek showed a general diffusion of fine gold in the gravel beds, but little concentrated in the deposits, and found in small quantities throughout the whole breadth of the valley.

In Spring Creek, the deposits showed a general diffusion of gold in nearly paying quantities through extensive gravel deposits. The water supply was considerable greater and the grade or descent of the valley sufficient to enable the deposits to be worked with much less expenditure of time or labor. These deposits were more valuable than French Creek. In Whiskey Creek the area drained by this stream was identical in character of the rocks of Spring Creek district, although less extensive. Gold was found in significant quantities in gravel deposits and its tributaries.

Gold was discovered in Castle Creek above the canyon in June 1875.it was found in small gravel deposits along the creek and in gulches leading into the stream from the south. About three miles below the point where Custer’s trail was leaving the valley, a bar covering an area of two acres gave some gold contents. It is believed that this deposit of gravel was 4 to 5 ft in thickness, was composed of quartz and slate pebbles, resting on bed rock of mica schists. Several pits were sunk in the flats near the channel of the stream, but failed to reach the bedrock owing to spring water, which could not be kept down by baling. Small gravel benches were found on the sides of the canyon below this bar, which gave until six colors of gold to the pan, but were of too limited area to be valuable.

In Rapid Creek, samples of quartz from the hills between Rapid and Box Elder Creeks gave 2 to 3 oz/t in a mortar and were characterized for showing gold particles of several colors. Gold was discovered in significant quantities in a number of places along this portion of the valley, but the miners did not open the placers and prospected the bars only enough to prove the presence of gold. These deposits of gravel including the high bars and narrow flats in the canyon are known to be valuable, resembling those of the Spring Creek District.