Mutating the seeds of groove ambience

“He not busy being born is busy dying,” wrote Bob Dylan -- and that could sum up the essence of Terry Riley.

Although UCLA Live was a little late Saturday night at Royce Hall with its celebration of Riley’s 70th birthday -- which occurred June 24 -- the long program caught the ever-questing spirit of Riley (and Dylan) perfectly, with young musical groups fearlessly, sometimes recklessly, mutating the seeds that Riley planted long ago. And the bearded, benign prophet of Minimalism was there too, busy transforming his music as well.

From the Bay Area came Matmos, a duo of bespectacled mad scientists who easily maneuvered Riley’s late-’60s electronic groove experiments into the electronica age with “For Terry Riley.”

It wasn’t that far a leap from such pieces as “A Rainbow in Curved Air” and “Happy Ending” to this musically arch-shaped audio-video collage, its compelling beat laced with sampled strands of the Kronos Quartet playing Riley’s “Sunrise of the Planetary Dream Collector.”

“A Rainbow in Curved Air” was also reborn Saturday, bracketed by a prelude and epilogue with a drum machine pounding out a bolero rhythm. While the original “Rainbow” recording -- heard in the background -- used the analog technology of its time, Riley now improvises on a digital Korg Triton synthesizer, which gave the piece a garish, gleaming timbre somewhat at odds with the old ecstatic floating ambience.

Despite its gigantic influence, “In C” -- like “The Rite of Spring,” to which it is often compared -- is really a one-off in which Riley, like Stravinsky, crystallized an idea in a single big bang and moved on. “In C” usually comes off as a playful communal celebration, no matter what combination of instruments. But in the metal-munching hands of Acid Mothers Temple, it was transformed into something relentless, aggressive, angry.

At first, this approach grooved marvelously; with its pitchless synthesizer swoops and the drums maintaining Riley’s pulse, it reminded me a bit of Miles Davis’ audacious electric jazz-funk, circa 1972. But the thrashing grew wearying after 40 minutes, partly because you couldn’t hear most of the 53 written motifs that gradually transform and shape the work. And it was loud -- loud enough for UCLA to distribute earplugs (alas, they quickly ran out)

Pianists Sarah Cahill and Joseph Kubera brought us more or less up to date with Riley’s current rambling writing for acoustic instruments with three pieces for piano four hands: “Jaztine,” “Tango Doble Ladiado” and “Etude From the Old Country.” And in a meditative interlude, Riley and his jazz-influenced guitarist son Gyan offered a pair of raga-flavored duo improvisations.