“Where did your long hair go? Where is the girl I used to know?”

—The Beach Boys, “Caroline, No”

“The ghost of electricity howls in the bones of her face”

—Bob Dylan, “Visions of Johanna”

Those lyrics say so much about two extraordinary masterpieces of the rock era—the Beach Boys’ Pet Sounds and Bob Dylan’s Blonde on Blonde, both, incredibly, released on May 16, 1966. In Dylan’s case, the release date is a matter of some contention, an amazing fact for an album of such historical significance. There’s reason to believe the album was not generally available to the public until some weeks later. Still, no other date has definitively risen to rival May 16th, which we might as may well regard as a traditional observance, sort of like Shakespeare’s birthday. And, regardless, the two albums, different as they are, stand Janus-like as markers of the end of one rock era and the beginning of another.

In 1966, Dylan was at the apex of his cultural significance. In the previous year he had reinvented popular music by “going electric” and releasing two albums of coruscating brilliance, Bringing It All Back Home and Highway 61 Revisited. He had, much to his chagrin, attained an importance that was as much symbolic as musical. More than a rock star, he had become a Bard. Young people pored over his lyrics with Talmudic zeal, searching for clues not merely to the complexities of the age but to the very meaning of life itself. It was a time when so much cultural heat surrounded Dylan that, in the wake of JFK’s murder, songwriter Phil Ochs could fear that Dylan himself might be assassinated. Just a few months after Blonde on Blonde’s release, Dylan dramatically withdrew from the public stage and retreated to Woodstock.

Blonde on Blonde only enhanced Dylan’s peerless stature. It was perhaps rock’s first double-album, its sprawl and lengthy songs (“Sad Eyed Lady of the Lowlands” occupied one entire vinyl side) emblems of Dylan’s outsized ambitions. The album’s gatefold cover, shot by Jerry Schatzberg, depicts Dylan from the hips up, wearing a worn, double-breasted suede jacket, a scarf tied around his neck, his hair an unruly halo of soft brown curls. Dylan is outdoors in Greenwich Village, staring directly into the camera, but the shot is out of focus, an eloquent reflection of Dylan’s persona at the time: impossibly poetic, grippingly present, but incapable of being fixed and fully comprehended. It is the sort of photograph that might more typically have graced a book by Ezra Pound or Allen Ginsberg.

The album’s songs, needless to say, eclipsed even the gargantuan expectations for Dylan at the time. He recorded the album in Nashville, itself a gesture of monumental impact – the most avant-garde figure in popular music invading the perceived citadel of retrograde conservatism. The city’s superbly talented session musicians teamed with such Dylan collaborators as keyboardist Al Kooper and guitarist Robbie Robertson to create a sound that could accommodate Dylan’s bluesiest, most rollicking rock & roll (“Leopard Skin Pillbox Hat,” “Absolutely Sweet Marie”) as well as serrated ballads of devastating intimacy (“Just Like a Woman”). Dylan described it best and most evocatively: “It’s that thin, that wild mercury sound. It’s metallic and bright gold, with whatever that conjures up.” His voice throughout the album is a hip, knowing snarl, wryly unsurprised by romantic perfidy (“I saw you making love with him/You forgot to close the garage door”), but desperately yearning for the transforming love of his lost Johanna or unattainable sad-eyed lady. A lyric like “You break just like a little girl” was at once painfully empathetic and a taunt.

If Dylan was somewhere between a seer and a poet in 1966, the Beach Boys were still struggling in a rapidly evolving pop culture universe to overcome their reputation among hipsters as cheesy, sun-and-fun hit-makers. Or at least Brian Wilson was. Inspired by the scope of the Beatles’ 1965 album Rubber Soul (whose track “Norwegian Wood” had also triggered Dylan’s “4th Time Around” on Blonde on Blonde), Wilson was determined to make an album that was similarly visionary and unified. Indeed, Pet Sounds began as a Brian Wilson solo album. Working intensely with lyricist Tony Asher and the brilliant set of Los Angeles studio musicians known as the Wrecking Crew, Wilson set out, he said, to explain “musically how I felt inside.”

That was no simple task. Wilson had already begun experimenting with psychedelic drugs and, after suffering debilitating panic attacks, he had stopped touring with the Beach Boys and became transfixed by the possibilities of studio recording. The emotions he longed to express combined crippling feelings of alienation (“I Just Wasn’t Made for These Times”) combined with a heartbreaking longing for life’s quotidian pleasures (“Wouldn’t It Be Nice”). As rock & roll stood on the brink of revolutionary transformations, Pet Sounds marinated in feelings of nostalgia and melancholy, the yearning for a world of wonder and innocence that would always be the same. Just as Dylan is haunted by his dream-vision of the elusive Johanna, Wilson longs for a beloved Caroline who will remain forever as she was. “I remember how you used to say/You’d never change, but that’s not true,” he sings. “Oh, Caroline, you break my heart.”

But, as Wilson has noted, if Pet Sounds is a concept album, it is a concept album of production. Phil Spector, Wilson’s idol, sought to create “little symphonies for the kids,” and Wilson pursued that same goal: the elevation of uncompromised adolescent emotions to ecstatic heights. Blonde on Blonde could scarcely contain itself on four album sides, while Pet Sounds is a tour de force of concision: thirteen songs in roughly thirty-six minutes. But in his luminous arrangements, Wilson made every second count. Without ever seeming contrived or overly clever, he guides each sonic moment into full, satisfying expression. Wilson employs harpsichords, car horns, flutes, strings, dog barks, glockenspiels, train sounds, the first use on a pop record of an electro-theremin and, of course, the Beach Boys’ lustrous harmonies to shape each song into its own spellbinding emotional universe.

But Pet Sounds, alas, was not made for its own time. If Blonde on Blonde was universally greeted as a work of genius, Pet Sounds elicited mystification, if not outright hostility. The other Beach Boys, most notably Mike Love, wondered why Wilson had wandered so far from the group’s hit-making formula. The band’s label, too, wondered where the hits were. Pet Sounds, which was quite expensive to produce, fell well short of commercial expectations. Capitol Records promptly assembled a best-of collection to keep the fans happy. The album garnered a more appreciative audience in the U.K., where, among many other prominent admirers, the Beatles used it as a spur to create their own next groundbreaking effort, Revolver.

It’s useful—and humbling—to keep in mind that Brian Wilson was twenty-three when he made Pet Sounds, and Dylan was twenty-four when he wrote Blonde on Blonde. Those two albums are rightly hailed as among the greatest rock albums in history, and they’ve helped shape every musical trend that has come in their wake. But it’s essential not to overstate that fact, or take it too literally. As musician and songwriter Ezra Furman said recently about Pet Sounds, “I never felt comfortable saying it had any influence on me. It’s so advanced that I find it rather embarrassing when the average mostly-amateur indie musician claims to be influenced by Pet Sounds. Really? It’s like the Ramones claiming to be influenced by Bach. I get that you listened to the album and loved it, but come on. You’re not operating on anything close to that level.” Word.

Related: Bob Dylan’s “Evolution of a Song” Feature Premieres on Genius