For nearly half a century, Johnny Cash was like a mighty black oak in the musical forest: strong, unbowed by the severest winds and seemingly immortal, easily overshadowing the bending willows and pines that surrounded him.

But in the years leading to his death on Sept. 12, 2003, Cash's mortality became evident in the intimate series of "American" recordings he began in 1994 with producer Rick Rubin, albums that ultimately generated five Grammy Awards for the Man in Black, nearly half his lifetime total.

On July 4, that series gained one more entry, "American V: A Hundred Highways," a collection Cash and Rubin began the day after "American IV: The Man Comes Around" was released in 2002, and which they worked on nearly until the day he died.

In the dozen songs on "American V," Cash's voice sounds even more frail, but if the force-of-nature power of his prime is often missing, in its place is an undeniable resolve and faith in his mission. From the content of those songs, that mission was to let the world in on the final thoughts of a giant of American music who knew the end was near.

It opens with Larry Gatlin's "Help Me," Cash's voice quavering and breaking, less singing than confessing the lyric's prayer: "With a humble heart on bended knee, / I'm begging you please, help me."

He sings Bruce Springsteen's "Further On (Up the Road)" as if it came from his own pen: "Got on my dead man's suit and my smilin' skull ring / My lucky graveyard boots and song to sing."

And it includes the final song written by Cash, "Like the 309." It joins the pantheon of songs about trains started at the beginning of his recording career:

"It should be a while

Before I see Doctor Death

So it would sure be nice

If I could get my breath

Well I'm not the cryin'

Nor the whinin' kind

'Till I hear the whistle

Of the 309."

It's the polar opposite of easy-listening music but carries right through to the end his penchant for brutal, unflinching honesty about the world and himself.

"I think it may be the best of all the 'American' series," Rubin says. "It really doesn't sound like any of the others — and I like them all. But this one really stands alone; it's very weighty and very serious."

Not that the previous "American" albums were the least bit flighty. The light moments that crop up on "A Hundred Highways" are those of a man smiling in the face of death or cherishing a loved one for the last time. It couldn't be much more obvious that Hugh Moffatt's "Rose of My Heart" is directed at the love of his life, June Carter Cash, who died just months before he did, and sung with the unsentimental love that made Rubin say of the album: "It's in a whole other realm. Some of it can stop you in your tracks."

It also stopped Rubin from working on it for a long time after Cash died.

"It was really emotionally difficult to go back to," he says. "But as we started working on it, and it became as beautiful as it ended up being, it felt fantastic. It was like he was here with us in the studio, guiding us, because everything came out of his vocals."

The selection of songs for "American V" Rubin says, "was pretty much in my hands, though we did talk a lot about it, and he'd tell me the ones he really liked, and usually the performances of those would follow. Those performances were really strong, so that made it that much more obvious which we would use."