GRANITE AT ENCHANTED ROCKS STATE PARK, TX
The outcrops at Enchanted Rock State Park, west of Austin, TX are part of a 250 km2 granitic batholit that intruded into Precambrian metamorphic rocks. The intrusion has been dated at 1046 +/- 12 Ma, i.e., mid-Proterozoic. Enchanted Rock itself is a smooth dome of granite that showcases spectacular erosion features.
Granites at Enchanted Rock are coarse-grained porphyritic monzogranites containing quartz (grey), microcline (pink), plagioclase (white) and biotite (black) belonging to the potassic calk-alkaline series. They are cross-cut by aplite dikes that intruded late, after cooling of the main granitic unit.
The dome at Enchanted Rock and neighbouring features are very smooth granite outcrops, with no soil, except in small circular features on top of the dome that host seasonal ponds.
Weathering on the sides of the domes produces large exfoliation sheets. They break into slabs that slides down or stay on top of the dome.
More erosion features...
Enchanted Rock State Park is also known for its dark skies - excellent place to watch the stars and the Moon.