They weren't the most important folk-rock group of the mid-'60s; the Byrds and others produced more enduring music. Yet the Mamas & the Papas were undoubtedly the most commercially successful folk-rock group of their time, racking up an astonishing nine Top 30 hits in little more than a year and a half. This 43-song double CD is by far the most comprehensive document of their legacy. It draws most heavily from their two 1966 albums (nine songs originate from their debut album, If You Can Believe Your Eyes and Ears, alone), when John Phillips' songwriting talent had yet to exhaust itself. Beyond the hits, the material is variable. Quite a few album tracks -- especially "Got a Feelin'," "Straight Shooter," "Go Where You Wanna Go," "Once Was a Time I Thought," and their cover of Lennon/McCartney's "I Call Your Name" -- were strong enough to have been hits under their own steam. Their slowed-down, California-ized versions of rock oldies were more problematic. And there's no doubt that their later material is less spirited and memorable than their initial burst of glory. The set includes various late-'60s and '70s solo recordings by each of the group's members (including small hit singles by John Phillips and Cass Elliott). Perhaps the most intriguing rarities are from the members' pre-Mamas days. These include commercial folk by the Big Three (featuring Cass Elliott) and primitive pop-folk-rock by the Mugwumps (including Elliott, Denny Doherty, and future Lovin' Spoonful member Zal Yanovsky).