SD Locations V4 - Association of Missouri Geologists

1 A Location Guide for Rock Hounds in the United States 437 SOUTH DAKOTA This northwestern Great Plains state varies from nearly level farmland to hill ridges, increasing steadily in elev. From 1,000 on the eastern border with Montana and Iowa to 3,500 along the western boundary with Wyoming. In the far western counties of Lawrence, Meade, Custer and Pennington the land rises abruptly into the 6,000 sq. mi. Black Hills region enclosed by the Belle Fourche and Cheyenne rivers.

2 These pine covered mountains, higher than the Alleghenies, culminate in Harney Peak in southern Pennington Co. At 7,242 this peak is the highest point in America east of the Rocky Mts. Cambrian rocks are exposed as thick bands around the entire mountain system. The rising granite mass intruded the famed Cretaceous Dakota sandstone, which underlies most of the Great Plains, and bent the broken edges sharply upward into steep hogbacks unusual in outward appearance. These hogbacks catch the regional precipitation and channel it into the underlying porous sandstone.

3 Laid down in Early Cretaceous times, as the continental seas were advancing from the south, the Dakota sandstone represents topset beds, wave reworked, and spread as a vast deltaic accumulation of water absorbing sands covering tens of thousands of sq. mi. with extraordinary homogeneity. Throughout the Great Plains, wells drilled deep into this unit provide an inexhaustible supply of cold artesian, Rocky Mountain snow melt water. Harney Peak is the crest of the geologically notable granite dome uplift which also produced a most remarkable series of pegmatite dikes ranking with those in Maine and Southern California for their production of gems and minerals.

4 The pegmatites are off shoots of the otherwise barren granite. From then have come some of the world s most spectacular crystals of Beryl and Spodumene. For instance, a single Spodumene crystal from the Etta Mine near Keystone on the east side of the Mount Rushmore National Memorial in Pennington Co. measured 42 long and weighed 90 tons. Also huge crystals of sparkling blue Beryl from the Black Hills pegmatites have measured from 18 to 27 long. In addition, gem Garnets, Quartz crystals, Topaz and Tourmaline add to the fascination of these pegmatites.

5 South Dakota 438 The commercial production of minerals, principally Gold, Silver, Copper, Iron, Lead, Manganese and Zinc, along with lesser amounts of Beryllium, Cesium, Lithium, Tantalum, Tin, Tungsten and Uranium has come only from the core of the Black Hills region. Two divisions are recognized: the Northern Section, centered in lead and Deadwood in Lawrence Co.; and a Southern Section, covering a somewhat larger area around Harney Peak. The northern section is characterized by vein deposits, while the Southern Hills Dist.

6 Includes both Veins and the extensive pegmatite dike exposures and mines. BON HOMME & CHARLES MIX COUNTIES SCOTLAND to WAGNER, regional rd. cuts, breaks, river banks, stream beds, excavations, etc. Selenite roses. BRULE COUNTY AREA: in the Oacoma zone of the Pierre Fm. On Elm Cr. Near its jct. with the Missouri River (about 15 mi. S of Chamberlain) gray Barite rosette up to 5 or 6 inches. CAMPBELL COUNTY MOUND CITY, W to the Missouri R., regional hillsides, ridges, cut banks, tributary gravels, etc.

7 Petrified wood, wood opal. CORSON COUNTY LITTLE EAGLE: area ridges, slopes, stream beds, etc. petrified wood, wood opal; along the Grand R. though entire Co., regional banks, breaks, gravels, etc. petrified wood, wood opal. A Location Guide for Rock Hounds in the United States 439 CUSTER COUNTY AREA: The November Mine, mi. SE of the Needles Eye Tunnel, on the W side of Hwy. 87 Arsenopyrite, Fluorapatite (fluorescent orange). BUFFALO GAP, entire region W 37 mi.

8 To the WY line, in stream gravels, cut banks, breaks, hillsides, etc. Fairfield agates. CUSTER: N, (1) near Laughing Water Cr., many area mines Columbite, Gold, Silver, etc.; and (2) Old Marble Quarry on the Needles Hwy. mi. NE Scheelite, and deep brown to black crystals of Sphene; E 6 mi., on French Cr., the Scott Rose Quartz Quarry Amblygonite (large yellow crystals), Aquamarine, Chrysoberyl, Quartz (milky, rose), Spodumene; W 7 mi.

9 , the Tin Mt. area, to Deer Camp rd., turn in mi.: (a) area mines, (b) in rocky uplift along side of rd., and (c) adjoining stream gravels gem Almandite garnets, Cassiterite, pale lavender crystals of Fluorapatite, Kasolite, Quartz crystals, Mica, Tourmaline and Zircon (reddish brown crystals); W 14 mi. on US 16 to Tepee Canyon, diggings on N of hwy. Extending up canyon agate, Beryl, Almandite garnets, Lepidolite, Staurolite, Tourmaline, etc.; E on US Alt. 16 for 15 to 17 mi.

10 (near Rte. 79), pegmatite outcrops Rose Quartz; S along US 385 for 32 mi. to Hot Springs in Fall River Co., all regional side rds., look for limestone outcrops and ridges Fairhill agates; in Bull Moose mine dump 5 mi. SE Barbosalite, exceptional reddish-violet crystals of Metastrengite, showy black and gold Pyrite, and Reddingite; at Beecher Lode mi. SE Amblygonite, Beryl, Lepidolite, Spodumene, blue-green Tourmaline; Gayle Royal Flush pegmatite, mi.