Thirty-three years have passed since the blessed otherworldliness of “Midnight at the Oasis.” Since then, Maria Muldaur has gone straight to heaven (with her various inspirational projects) and, thank God, also to hell, proving herself one of the grittiest, gutsiest, most lowdown blueswomen of her era. Yet, as bold and blisteringly good as Muldaur’s blues output has been throughout the last few decades, it all seems a mere prelude to the swampy majesty of this aptly titled collection. On her two previous discs for Stony Plain (both Grammy-nominated), Muldaur trolled the classic country-blues repertoire of the 1920s, ’30s and ’40s. Here, the material is chronologically akin, but shifts from rural to urban, spotlighting the racy material, often heavily spiced with risqué double entendres, made famous by such seminal figures as Ethel Waters, Sippie Wallace, Mamie Smith and Victoria Spivey. Reinforcing her musical passion for all things Louisianan with a blazing “New Orleans Hop Scop Blues” and rivaling another blues queen, Dinah Washington, with her winking readings of “Up the Country Blues,” “A Good Man Is Hard to Find,” “Handy Man Blues” and “One Hour Mama,” Muldaur is the equal of all the legends she salutes. But the disc’s pièce de résistance places her in more contemporary company, as she goes tonsil-to-tonsil with Bonnie Raitt on a blow-the-roof-off-the-woodshed treatment of Wallace’s “Separation Blues” so devilishly good it’s positively heavenly.