It’s all the Melvins’ fault. Not only did Washington’s eccentric underground rock heroes lay the foundation for grunge, they also birthed the kicking, screaming, unwashed child that became sludge. Fermenting somewhere between doom metal and noisy punk, the genre mashes up slow tempos and churning, detuned guitars, a stew that may have originated with Buzz Osborne and co., but was perfected in the sweltering swamplands of Louisiana. Sludge trailblazers like Eyehategod turned up the throat-shredding nihilism and ear-splitting feedback, while Crowbar and Acid Bath injected dark melodies through the stentorian vocals of Kirk Windstein and Dax Riggs, respectively. North Carolina’s Corrosion of Conformity and New Orleans supergroup Down—boasting members of Pantera, Crowbar and Eyehategod—added a Southern rock patina to sludge’s caustic brew, landing major-label endorsements in the process. The genre’s thick, greasy legacy continues with Weedeater and Black Tusk, and can be heard in the early work of Mastodon and High On Fire, all of whom have since branched out in different directions.