The Black Hills area in South Dakota is among the top five localities in the United States for variety of rocks and minerals.
In addition to agate and rose quartz, there are more than 40 other minerals found here: including copper, silver, lead, tin, feldspar, spodumene, beryl, mica, quartz and gold. There are also vast deposits of iron, alabaster, gypsum and limestone in the Black Hills. The alabaster and gypsum are found in the red clays surrounding the Hills. The principle limestone canyons are in the western part of the Black Hills near the Wyoming border. In these scenic canyons are deposits of colorful agates, with the multi-colored Tepee Canyon Agate being the most popular.
The most sought after agate from South Dakota is Fairburn Agate. It is named after a city 10 miles to the west of the deposit in Custer County. This colorful thin banded Agate was named the State gemstone in 1966. Also found in the same area are Banded Jasper, Rose Quartz, Prairie Agate, Blue Chalcedony, Bubble Gum Agate, Puddingstone Conglomerate, Petrified Wood, Water Agate, Black Agate and Moss Agate. The rock beds are scattered in eroded areas near Kadoka, Interior, Scenic, and Fairburn. A wide variety of agate can be found in the gravel pits in the entire eastern part of the State.
It is said there was more Rose Quartz found in Black Hills mines than any other area in the world. Rose Quartz was named the official mineral of the State of South Dakota in 1966. The nation's largest gold mine, The Homestake Gold Mine is in Lead, South Dakota, in the northern portion of the Black Hills. Before its closing in 2002, the Homestake Gold Mine was the oldest, largest and deepest mine in the Western Hemisphere, reaching more than 8000 feet below the town of Lead.
South Dakota is also home to many fossils. Prior to 1988, South Dakota's state fossil was the cycad, a type of palm-like Mesozoic plant known from the Cycad National Monument near Minnekahta. Unfortunately illegal collecting and vandalism destroyed the Monument. In 1988, South Dakota changed the designation to Triceratops as its official state fossil.
There are lots of great rockhounding spots and pay for diggings sites in South Dakota. It seems to be a friendly state for doing so, and there is lots of information available on the web. Just do a South Dakota rockhounding search. Just be sure to check with local authorities so you don't get into any trouble.
See my page on Rockhounding Rules for general information on the rules of collecting rocks on various lands.