“Asbestos was there for hundreds, if not thousands, of years, and that has not translated into negative health effects,” said Dr. Ihsan Azzam, the state epidemiologist.

Image Brenda Buck and Rodney Metcalf found asbestos on rocks and soil near Las Vegas. Credit... Isaac Brekken for The New York Times

Naturally occurring asbestos deposits are not uncommon, and in past decades, particularly rich veins were mined for commercial use. It proved to be a dangerous occupation: Asbestos fibers travel easily through the air and are easily inhaled, scientists later found, embedding themselves in the lungs.

Once there, even in modest amounts, the fibers set off a cascade of inflammatory effects that can lead decades later to lung cancer, mesothelioma and other respiratory ailments. One study conducted a few years ago found that one-fifth of the residents of Libby, Mont., the site of a large vermiculite mining operation, sustained asbestos-related lung diseases. Many never worked in the mines.

The Environmental Protection Agency designated the area a Superfund site in 2002 and, with the Department of Health and Human Services, declared a public health emergency there in 2009.

The growing body of research into asbestos exposure inspired Dr. Buck and Dr. Metcalf to take a closer look at their home state. In October 2013, they published a study finding that natural asbestos-bearing mineral deposits were abundant in the region, from the southern shore of Lake Mead to the edges of the McCullough Range.

In a follow-up analysis, Dr. Metcalf and Dr. Buck reported that asbestos fibers around Boulder City and the eastern part of Henderson and Las Vegas were similar in shape and size to those sickening people in Libby. And last month, the two geologists published a paper showing that a continuous swath of natural asbestos runs from Nevada into neighboring Arizona.

The findings have already had consequences. The Nevada Department of Transportation delayed construction of a $490 million highway project, called the Boulder City Bypass, after learning that it would run through an area that the scientists had found to be rich in asbestos.