Texas Hill Country’s Enchanted Rock

June 28, 2018


June 2018 Viewer's ChoicePhotographer: Patti Weeks
Summary Author: Patti Weeks 

Enchanted Rock is the second largest pink granite monadnock in the United States. Designated in 1936 as a Recorded Texas Historic Landmark and in 2014 as an International Dark Sky Park, Enchanted Rock State Natural Area occupies a remote section of the Hill Country in central Texas, along with a scattering of cattle ranches, 500 plant species and abundant wildlife

BOTTOMThis igneous rock mass, or pluton, located in the Llano Uplift, was pushed up into the overlying sedimentary Cretaceous Edwards limestone from a large magma pool, which was estimated to be 7 mi (11 km) below the surface one billion years ago.

The Enchanted Rock dome is the visible part of a huge batholith, called the Town Mountain Granite. At an elevation of 1,825 ft  (556 m) above sea level, the dome rises 425 ft (130 m) above the base elevation. It covers 640 acres (259 hectares), but it's just a small part of the 62 sq mi (161 sq km) underground batholith. Enchanted Rock is an exfoliation dome, with sheets of rock peeling off like layers of an onion. After the overlying sedimentary rock was eroded away, the load on the dome decreased, allowing it to expand and then break into smaller sections and begin sliding down the dome’s sloped sides.

The 15 tiny dots in the top photo are visitors who are hiking the Summit Trail to the top of the dome. The hikers will see the fragile vernal pools, ecologically threatened depressions of flora and fauna, which include rock quillwort and tiny fairy shrimp. Some onion peels and tumbled boulders are visible in the top photo. The bottom photo shows lower-lying hoodoos that have been eroded through differential weathering of the exposed layers of rocks that have slid or tumbled down the dome. Photos taken May 9, 2018. 

Photo Details: Top - SONY DSC-HX400V camera; 1/800 sec. exposure; ƒ/3.5 aperture; ISO 80; Focal Length: 11.86 mm focal length; 4.3-215mm ƒ/2.8-6.3. Insert - same except: 1/500 sec. exposure; Aperture: ƒ/5 aperture; 53.33 mm focal length.