Every El Pasoan has looked up at the Franklin Mountains at some point and felt something difficult to name. Something old. Something watching. If you have ever driven up Scenic Drive at sunset and caught that dark rust-colored shape spreading across the face of South Franklin Mountain, wings outstretched, head turned to the side, you already know what we are talking about.
That is the Thunderbird. And it has been there a lot longer than El Paso has.
The Shape in the Mountain Is Made of Some of the Oldest Rock in Texas
The Thunderbird formation on the southwest face of Franklin Mountain is not painted on, and it is not a trick of the light. The shape is formed by reddish-brown Precambrian rhyolite, a volcanic rock rich in silica and quartz, set against the surrounding gray limestone of the El Paso Group. Two different rock types and colors come together to form one unmistakable silhouette.
That rhyolite is approximately 950 million years old. The Castner Marble it sits above, the oldest rock unit in the Franklin Mountains, formed about 1.2 billion years ago, making it some of the oldest exposed rock in the entire state of Texas. To put that in perspective, multicellular life did not exist yet when these rocks were formed. The dinosaurs would not show up for another 800 million years. The Franklin Mountains were already ancient before the concept of ancient had any meaning…