Step back 1.3 billion years in Llano County

Visitors to Enchanted Rock State Natural Area trek to the top of the massive, granite dome, part of a 1.3 billion-year-old batholith. Photo by Jennifer Greenwell

You don’t need a time machine to tread Precambrian ground in Llano County. While the area is known for its white-tailed deer population and namesake Llano River, it has another, much older claim to fame: 1.3 billion-year-old rocks. 

Located center stage on the Llano Uplift, a patch of exposed Precambrian rock, Llano County is a destination for geologists and rockhounds.

The uplift was created when a portion of granite below Earth’s surface became superheated, liquified, bubbled up, and then cooled underground. Several million years of erosion unveiled the once-molten granite that can be seen throughout Llano County. What makes the Llano Uplift fascinating to geologists is it is completely unchanged since its formation over a billion years ago—a clear, unaltered glimpse of the Precambrian Era. 

Llano is popular ground for rockhounds. Llanite (Llano rhyolite), a rare type of igneous rock thought only to exist in the Llano Uplift region, was first identified in the area. The extremely hard rock primarily consists of blue quartz (a rare quartz color), orthoclase feldspar, and biotite mica. 

Now that you know, get ready to go. 

Enchanted Rock State Natural Area showcases a batholith, a massive igneous intrusion formed below the surface. The batholith, which includes Enchanted Rock and Granite Mountain in Marble Falls, measures at least 40 square-miles across. Its exposed portion is 12 miles by 20 miles; the remaining portion is below ground. It is believed this batholith was originally formed 2-4 miles below the surface. Enchanted Rock State Natural Area’s series of granite hills includes Little Mountain, Turkey Peak, Freshman Mountain, Buzzard’s Roost, Flagpole Mountain, and, of course, the largest one, Enchanted Rock.

An aplite dike in the granite at Grenwelge Park on the Llano River in Llano. Photo by Jennifer Greenwell

Grenwelge Park on East Haynie Street at the bridge in Llano is free to explore. You will find evidence of fascinating geologic events such as igneous intrusion, folds, boudinage, and more. You might even spot one of the 241 different types of rocks and minerals known to be in the area. The riverbed is a great place to look for rocks. The Kingsland Slab, where FM 3404 crosses the Llano River in Kingsland, is another rocky riverbed worth exploring.

Rockhounds will have a ton of fun exploring the Llano Riverbed at The Slab in Kingsland. Photo by Jennifer Greenwell

The overlook at Lookout Mountain, located on RR 1431 between Granite Shoals and Kingsland, has a beautiful view of Lake LBJ. But if you turn around, you’ll see a geologic snapshot from millions of years ago. The mountain was sliced when the road was constructed, revealing rock layers and faults. The faults happened 540 million years ago when Africa and South America collided with the southern part of North America. 

Check out the exposed outcrop of llanite at the Llanite Dike 9 miles north of Llano on Texas 16 near Baby Head Mountain. A dike is a sheet of rock formed in a fracture of pre-existing rock. The Llanite Dike is believed to be a sheet intrusion, which is created when molten rock fills a crack and then solidifies into a sheet. The formation of llanite continues to be a topic of discussion among geologists. The Llanite Dike in Llano County is one of the most famous dikes in Texas and thought to be one of the youngest Precambrian intrusive bodies in the Llano Uplift. 

An afternoon adventure in search of Precambrian rocks is yours for the taking in Llano County.