Abandoned houses in Picher, Oklahoma. Considered too toxic to be habitable, the once-booming lead- and zinc-mining town was declared a Superfund site in 1981, but most of the residents didn’t leave until 2006. The EPA has called the city, now a ghost town, the "most toxic place in America." (Seph Lawless)

Photographer Seph Lawless is no stranger to post-apocalyptic settings. He has photographed the eerie remains of abandoned places across the country—from a football stadium in Ohio to an amusement park in North Carolina. But perhaps none of these urban ruins are as dangerous as that of a tiny ghost town he recently visited and documented—the once-booming lead- and zinc-mining town of Picher, Oklahoma, which the Environmental Protection Agency (EPA) called the "most toxic place in America."

At its peak in the 1920s, Picher was the center of the Tri-State Mining District, a rural area of Oklahoma, Kansas and Missouri that was the lead and zinc capital of the world and boasted a population of nearly 20,000 people. But in 1981, the EPA declared the area a federal Superfund hazardous waste site, where "chat" piles—lead-laced mountains of crushed limestone, dolomite and silica-laden sedimentary rock—dominate the landscape. In 2008, a tornado further devastated Picher, and its few remaining residents. In 2009, the town ceased municipal operations. Today, Picher is a ghost town.

"As I walked through [the town], it was eerily quiet," Lawless, who visited and photographed Picher in June 2015, said. "I didn't hear anything, not even a bird, everything was dead here."

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But there's more to the town than eerie silence, empty homes and toxic waste. Lawless experienced another real danger wreaking havoc on the city. Years of mining and carving tunnels beneath the town have left giant sinkholes throughout the area, making buildings, houses and roads susceptible to sudden collapse.

"I kept thinking the earth could open up any minute and swallow me and no one would ever know," Lawless said. "At one point my foot went through the ground and I fell to the ground thinking I was going to cave in and die."

And there were another danger, but this time, it was not limited to Picher (or Oklahoma). While capturing images of the town, which will appear in his new book The Prelude: the Deadliest City in America, Lawless could see a storm brewing. The dark clouds would further give an ominous and haunting feel to the eerie photos he shot of the ghost town, but Lawless knew it was better to be safe than sorry.

"I looked up and just started driving in the opposite direction just to avoid the storm since it was tornado season," he said. "I was just going as fast as I could to get away from it."

Click through the slideshow above for a photographic tour of Picher, Oklahoma by Seph Lawless. For more on Lawless' work, visit his website or follow him on Facebook, Instagram and on Twitter.