An area in the U.S. Southwest that’s about half the size of Connecticut has emitted the country’s largest concentration of methane, a potent greenhouse gas, according to a new analysis of satellite data.

The study, which was released jointly by the American Geophysical Union and NASA, found that between 2003 and 2009, the area released .59 million metric tons of methane each year, which is more than triple the standard estimate for an area of that size. The 2,500-square-mile (6,500 square kilometers) spot lies near the intersection of Arizona, New Mexico, Colorado and Utah.

The hot spot emerged before the rise of hydraulic fracturing, a practice that has spurred concerns about “fugitive” methane emissions—leaks that occur while fracking is under way.