One of the most stunning, fully realized debuts of the young 21st century, Fleet Foxes' self-titled album (and its accompanying Sun Giant EP) combined CSNY-style folk with Beach Boys harmonies and it came right smack in the middle of a rich time for both folk and psych pop. It was released just months after breakthrough folk debuts by Bon Iver and The Tallest Man on Earth, and less than a year before modern psych-pop classics like Grizzly Bear's Veckatimest and Animal Collective's Merriweather Post Pavillion. Its followup album, 2011's Helplessness Blues, proved even further that Fleet Foxes were masters of '60s/'70s psychedelic folk. With the eight-minute "The Shrine / An Argument," they showed off a real knack for progressive folk too.

Then Fleet Foxes disappeared, and a lot changed. The 2008-era indie folk class slowly distanced itself from folk music and the mainstream world began co-opting it. Mumford & Sons won a Grammy for Album of the Year. Bands like The Lumineers and Of Monsters & Men entered the picture with watered-down takes on Fleet Foxes' harmony-fueled folk and quickly got very popular. While that was all going on, Bon Iver started making wacky electronic music and former Fleet Foxes drummer Josh Tillman became very famous as the Harry Nilsson-esque Father John Misty.

For Fleet Foxes to make a comeback in 2017, it would seem like there'd be potential for them to either cash in on the mainstreamized version of their own music or ditch it entirely like Bon Iver. Instead, Fleet Foxes did neither. They dove even deeper in the realm of '60s and '70s psychedelic folk. It's probably not a sound that's going to gain them more fame, but it's a sound that's being kept alive by a new generation of acclaimed indie artists. A newer student of '60s folk, Angel Olsen, released one of the best albums of last year -- maybe the best. The past few months have also seen well-received breakthroughs by Big Thief, Julie Byrne, and Weyes Blood that all pull from that same era and style. (Not to mention the indie world likes the Grateful Dead now.) Perhaps those artists' fanbases will welcome Fleet Foxes' long-awaited third album with open arms. If they do, they'll likely be very satisfied.

Crack-Up picks up right where Helplessness Blues, and particularly "The Shrine / An Argument," left off. It opens with a three-part song ("I Am All That I Need / Arroyo Seco / Thumbprint Scar"). That's followed by a track ("Cassius") that segues right into another track ("Naiads, Cassadies") with the tracklist written out like a Grateful Dead setlist (only using a hyphen instead of an arrow). Two songs later is lead single "Third of May / Odaigahara," another two-parter that's nearly nine minutes long. If their debut is their pop album and Helplessness Blues is their more traditional folk album, this is their prog album. With the help of a string quartet on some songs, they near Renaissance territory. The arrangements on Crack-Up are among the most ambitious of Fleet Foxes' career. They clearly weren't content to repeat any previous ideas. If Fleet Foxes were going to come back, they were going to take a giant step forward.

The trend with Fleet Foxes albums seems to be that each one will be a little less immediate, each one will challenge the listener a bit more. That's true of Crack-Up, which requires patience and has no White Winter Hymnals in sight. That said, Robin Pecknold is a pop songwriter at heart and a truly gifted singer, and both of those things stop the album from ever coming off as "boring." He and his similarly gifted backup singers still sound as rich as they did on their debut. When the full band kicks in on the opening song, they sound as lush and uplifting as they ever have. One of the album's softest songs is also one of its catchiest, "If You Need To, Keep Time on Me," which sounds like the light of day after the murky ending of "Third of May / Odaigahara." An unsurprising choice for lead single, "Third of May / Odaigahara" is quite possibly the album's highest point, trekking through lightness and darkness, accessibility and experimentation -- without ever losing sight of its vision. That song's not the only time Fleet Foxes get a little weird either. The darker and more off-kilter songs like "Naiads, Cassadies," "Mearcstapa," and "I Should See Memphis" are as essential to Crack-Up as the brighter songs. Then there's the songs that do both, like "Fool's Errand." That song is one of the album's closest moments to "classic" Fleet Foxes, with a head-nodding verse exploding into a blissful chorus -- making it one of the only verse-chorus-verse songs on the album -- while still favoring more unusual melodies. It's a fine representation of the push and pull Fleet Foxes display on this album. They're breaking the confines of traditional songwriting without forgetting how to write a great song.

Crack-Up officially comes out this Friday (6/16) via Nonesuch, but until then you can stream it here.

UPDATE (6/16): It's out now. Listen:

More From Brooklyn Vegan