The Trailist: Canyon Lake Gorge offers a view of normally hidden geology

Growing up in the Southwest, I’ve seen many canyons carved by the steady flow of water over millions of years. Until this week, I had never visited a canyon that formed in only a few days. 

Canyon Lake Gorge is a 64-acre preserve owned by the U.S. Army Corps of Engineers but leased to the Guadalupe-Blanco River Authority (GBRA). Swimming and freely roaming the gorge are prohibited, but the GBRA and the nonprofit Gorge Preservation Society in November completed a self-guided overlook trail along the canyon’s north slope. 

Although the trail is short, I came away convinced that residents of Texas’ Interstate 35 corridor should visit at least once to better understand the impact of flooding and how water works in our region. It’s one thing to know that water in the Hill Country weaves its way between surface and subsurface, but that’s not the same as seeing it up close.

The gorge owes its existence to the massive 2002 floods, some of the most deadly and destructive in Texas history. An entire year’s worth of rain fell over one June week on the hills of the upper Guadalupe River watershed, filling Canyon Lake to the brim for the first time since its construction in the 1960s. The water poured over the spillway and carved more than a mile of canyon in about three days, according to scientists.

When this torrent ripped away 40 feet of vegetation, topsoil and rock, it allowed visitors to see springs, seeps, faults and fractures that define the more than 100-million-year-old geology of the Texas Hill Country.

Entrance fees to walk the trails alone are $5 per person. Next time, I would instead spend the $15 to take the 90-minute tour or $20 for the three-hour version. The GBRA also offers educational tours and outdoor classrooms for $5 per student.

The 0.62-mile out-and-back trail follows the east side of the gorge, passing pools, waterfalls and the dry patches between them where water disappears underground. It connects eight viewpoints with benches and interpretive signs and restrooms at both ends. The trail dead-ends at the final overlook below the Canyon Dam spillway.

Another short path called the Plant Trail makes a loop near the main trail entrance.
Visitors on the self-guided route must stay on the main trail and can’t walk down into the gorge below. I immediately regretted not booking the guided tour to see the fossil-studded rock and dinosaur tracks up close. Even looking down from above, it’s obvious that Canyon Lake Gorge reveals geological secrets that only cavers or road-cutters typically see.

My favorite viewpoint looked down on the Hidden Valley Fault Zone, where a band of sedimentary rock of a different color and composition than the adjacent limestone, has shifted downward 180 feet. The fault is part of the Balcones Fault Zone, formed 25 million years ago and the reason for the Great Springs of the Edwards Aquifer — San Antonio, Comal, San Marcos and Barton among them. At the gorge, visitors can see the water pop out of a spring, pool up along the fault zone, drop underground, then reappear at another spring in a short span.

Another viewpoint looked down on bizarrely patterned fractures that channel water in rectangular patterns around dry patches of rock. During my reporting on local water issues, I had heard many stories of a driller sinking a dry water well into what’s supposed to be a productive aquifer. The driller then tries again several feet away from the dry well and taps a gusher. This made a lot more sense after seeing these patterns on the surface.

When I got home, I looked up a satellite image from 1998 that showed the area downstream of the spillway blanketed in trees, looking like any other Hill Country ravine. It further reinforced the knowledge that water winds its way unpredictably under our feet across the whole region, not just at Canyon Lake Gorge.

This story has been updated to clarify a reference to Canyon Lake’s spillway.