The upper Arkansas River valley, including the area around Granite, is hemmed in between high, sheer rock outcroppings of buff/pink-colored Precambrian granite. Granite lies at the center of the Colorado Mineral Belt (CMB), a 50 mile-wide strip that runs north and south for 300 miles. Mineralization of the CMB came primarily by way of intrusions of Tertiary Period magmas. The primary ores of the CMB were generally deposited as mixed metal sulfide mineral veins containing pyrite, galena, sphalerite, chalcopyrite, and gold, silver, and copper. During the last glacial period native gold was freed from the host rock and deposited along the ancient roaring Arkansas River bed - much larger than it is today due to the melting glacial runoff.