Llano Uplift
The Llano Uplift is a geologically ancient, low geologic dome that is about 90 miles (140 km) in diameter and located mostly in Llano, Mason, San Saba, Gillespie, and Blanco counties, Texas. It consists of an island-like exposure of Precambrian igneous and metamorphic rocks surrounded by outcrops of Paleozoic and Cretaceous sedimentary strata. At their widest, the exposed Precambrian rocks extend about 65 miles (105 km) westward from the valley of the Colorado River and beneath a broad, gentle topographic basin drained by the Llano River. The subdued topographic basin is underlain by Precambrian rocks and bordered by a discontinuous rim of flat-topped hills. These hills are the dissected edge of the Edwards Plateau, which consist of overlying Cretaceous sedimentary strata. Within this basin and along its margin are down-faulted blocks and erosional remnants of Paleozoic strata which form prominent hills.
| Llano Uplift | |
|---|---|
location of Llano Uplift in Texas | |
| Geography | |
| Country | United States |
| State | Texas |
| Region | Texas Hill Country |
| County | Llano County |
| Municipality | Llano, Texas |
| Range coordinates | 30°10′27″N 99°03′55″W |
| Geology | |
| Orogeny | Grenville orogeny |
| Age of rock | Mesoproterozoic |
| Type of rock | Precambrian and Paleozoic inlier surrounded by Cretaceous uplands. |
The Llano Uplift is well known for its large, granite domes, such as Enchanted Rock. The area includes several major rock quarries like Granite Mountain that mine the distinctive pink granite. Further, the area contains the only known deposits of llanite.
In 1992, the Texas Department of Health identified the area as one of four regions with high potential for the presence of hazardous levels of radon gas.