If you were to set foot in the Sevier Valley in Utah, the landscape might look deceptively still. However, beneath that quiet is a loud history, and the geologists at the Utah Geological Survey now have a way to read it.
Using lidar, UGS Project Geologist Adam I. Hiscock and his colleagues have spent years painstakingly remapping the active faults that crisscross central Utah. What they've found is both illuminating and sobering: the region's earthquake hazard is more complex and more present than older maps ever showed.
The Tool That Changed Everything
Before lidar, fault mapping was hard, imprecise work. Geologists relied on aerial photographs, paper topographic maps, and long days of fieldwork to trace the subtle scars that earthquakes can leave on the landscape. These scars, known as fault scarps, are step-like features formed when the earth ruptures along a fault line during a major earthquake. Small ones, or those hidden beneath thick vegetation, were easy to miss until lidar changed the equation entirely.
By sending out millions of laser pulses from aircraft and measuring how long each one takes to bounce back, lidar can digitally strip away trees and brush to reveal the bare earth surface beneath. The result is a strikingly detailed three-dimensional model of the ground, one that exposes fault scarps that have been quietly sitting there for thousands of years, invisible to previous methods.
"Lidar is an incredibly powerful tool," says Hiscock. "Being able to generate a 'bare earth' 3D model of the ground surface and see through vegetation allows us to map very small and eroded fault scarps that were previously impossible to detect using older methods."
The new mapping, which covers parts of six counties: Garfield, Juab, Millard, Piute, Sanpete, and Sevier, reveals more detail and complexity than anything produced before. Faults that were vaguely outlined on older maps now appear with sharp precision. New fault segments that were never mapped at all have come into view.
A Region With a Seismic Past
Central Utah sits at a geological crossroads. The region spans the transition zone between the actively extending Basin and Range Province to the west, where the crust is literally being pulled apart, and the stable Colorado Plateau to the east. That tectonic tension has made the area a historically active earthquake zone.
Two of Utah's largest historical earthquakes struck right here: a magnitude 6.6 event near the Tushar Mountains in 1901 and a magnitude 6.0 earthquake near Elsinore in 1921. Both were felt widely across the region, with damage reported throughout the Sevier Valley. They are reminders that central Utah's faults are not dormant relics of the distant past; they are active systems capable of producing powerful earthquakes.
Despite the dangers, for years the faults responsible for that seismic activity were only roughly mapped. The new lidar-based work changes this situation by providing what Hiscock describes as "foundational knowledge" for rapidly growing communities that are building infrastructure intended to last for generations.
Boots on the Ground
For all its power, lidar is not a substitute for fieldwork. One of Hiscock's strongest convictions, and a lesson he'd pass on to any geospatial professional, is that the technology works best when paired with human judgment and direct observation.
"I feel strongly that it is always important to put 'boots on the ground' and check many of the fault scarps and other features you're mapping on a computer," he says. "Field checking your mapping is essential."
That combination of bird's-eye precision from lidar and the ground-level intuition of an experienced geologist is what gives new maps their credibility. Each significant feature identified in the data was verified in the field, ensuring that what appears on the final maps reflects reality, not just a shadow in the data.
Drawing the Safety Zones
The maps themselves are only part of the project's value. Alongside each mapped fault trace, the UGS team created recommended surface-fault-rupture special-study zones—advisory areas where a site-specific geological investigation is recommended before new development begins.
These zones are not regulations. The UGS is a non-regulatory agency, and it cannot mandate what gets built where. But by drawing these boundaries and making them available to city and county planners, the agency gives local governments a concrete, science-based tool for making smarter decisions about growth.
"We provide these zones as recommendations to help ensure safer and smarter community growth," says Hiscock, "and provide essential guidance for city and county planners to create and enforce geologic hazard ordinances."
For communities that may not think of themselves as "earthquake country," that guidance matters. Rural Utah has seen significant population growth recently, and development is expanding into areas that haven't historically been subject to the same level of scrutiny as the Wasatch Front. The new maps help close that gap.
Getting Communities to Listen
Science that sits in a report and never reaches the people it's meant to protect has limited value. That's why outreach is a core part of the UGS mission and why Hiscock is candid about the challenges of communicating seismic risk to communities that don't always see themselves as vulnerable.
"Geologic hazards don't exist in a vacuum," he says. "It is just as important to communicate our science as it is to actually do the research."
The UGS has developed a range of public-facing resources, including Putting Down Roots in Earthquake Country, a comprehensive guide to earthquake preparedness. The agency also offers a model geologic hazard ordinance to help municipal and county governments translate scientific findings into local policy.
The goal is to make the science accessible to various groups like homeowners wondering about the land beneath their house, developers planning a new subdivision, or elected officials who need to weigh growth against risk.
What Comes Next
The central Utah project is part of a decade-long effort by the UGS to update fault mapping across the state. Most of the work near Utah's most urbanized corridors, including the Wasatch Fault in northern Utah, is now complete. The agency is shifting its focus to areas with lower current populations but significant potential for future development.
That shift reflects a longer-term vision: getting ahead of growth rather than reacting to it. The new fault maps also guide decisions about where to conduct paleoseismic research—detailed studies of ancient earthquakes recorded in the geologic record—which can help scientists determine how often faults rupture and what magnitude of earthquake they're capable of producing.
"This mapping guides us in selecting sites for further paleoseismic research," Hiscock explains, "which allows us to determine fault activity rates and model earthquake probabilities."
The Data is Available Now
All of the data from the central Utah fault mapping project is publicly available. The final report, including detailed fault maps and surface-fault-rupture special-study zones, can be accessed through the Utah Geologic Hazards Portal. A full GIS geodatabase and detailed report are also available here.
The portal serves as a living resource, giving anyone from a first-time homebuyer to a county engineer access to the most current understanding of Utah's geologic hazards.
The fault lines have always been there. Now, for the first time, we can see them clearly.
Adam I. Hiscock, P.G., is a project geologist with the Utah Geological Survey's Geologic Hazards Program. For more information on earthquake hazards in Utah, visit geology.utah.gov/hazards.
