NEW YORK -- Fans of the late Johnny Cash have a lot to keep them occupied: A box set being released Tuesday contains a staggering 64 never-heard-before recordings.
The five-disc box, "Unearthed," is all material recorded during the last decade, during Cash's fruitful partnership with Rick Rubin, who had been known best as a rap and rock producer.
Cash died Sept. 12 at age 71 of complications from diabetes.
"It seems like a nice punctuation," Rubin said. "It seems like a bookend with the beginning of his career and the Sun (Records) work. It's a beautiful way to sum things up."
The set includes a duet with the late Joe Strummer on Bob Marley's "Redemption Song," and collaborations with Fiona Apple, Nick Cave, Carl Perkins and Glen Campbell. Cash tackles two Neil Young songs, "Heart of Gold" and "Pocahontas," as well as material by Kris Kristofferson, Dolly Parton, Steve Earle, Roy Orbison, Chuck Berry and Willie Nelson.
The Cash-Rubin collaboration seemed like an odd one: a long-haired, somewhat mysterious impresario who was one of rap's behind-the-scenes pioneers and a music legend who had been largely written off as a contemporary recording artist.
But a mutual love of music enabled them to overcome differences. Cash responded to Rubin's desire to record him largely unadorned, and their musical open-mindedness took them down intriguing paths.
"When he was too ill to continue being on the road, that affected him," Rubin said. "It was a large part of his life, communicating with people on a regular basis. He took all that energy and put it into record-making. It was his reason to exist."
Cash participated in the making of "Unearthed," finished just before he died. He offered reflections on each of the new songs in the liner notes.
Rubin would send Cash CD after CD of song suggestions before each of the recording sessions, and they tried a lot. (Not every idea: Rubin, unsuccessfully, kept trying to get Cash to make a version of Radiohead's "Creep.")
This meant a huge amount of outtakes, and they fill three of the five "Unearthed" discs. A handful can rightly be called failures; Cash misses the essence of Earle's "The Devil's Right Hand," for instance.
But many were cut simply because they didn't fit the concept of a particular album. On most of the second disc, Cash is backed by Tom Petty and the Heartbreakers, and he works with three members of the Red Hot Chili Peppers on Young's "Heart of Gold."
The fourth disc is an entirely new gospel album, "My Mother's Hymn Book," which Cash describes in his liner notes as "my favorite album I've ever made."
"I nailed it," Cash said. "That was me. Me and the guitar, and that's all there was in it and all there was to it. I'm so glad that I got that done."
The fifth disc is the only one with previously released material: a collection of highlights from the four-album American Recordings series.
"It's a lot of material," Rubin said. "Most box sets are mostly a collection of material that's already been out. This is like getting four brand new albums all at once."
At some point, Cash's record company may break up the box set into smaller, more affordable chunks (list price is $78.98), but there are no clear plans for that, Rubin said.
Cash may soon rival Tupac Shakur as one of the most prolific posthumous artists. In preparation for the fifth disc in the American Recordings sequence, he recorded some 50 new songs after his wife, June Carter Cash, died in May. None of these songs appear on "Unearthed."
"I think he would have continued doing this for a long time," Rubin said.