The Crumb-like metallic sounds returned to end the movement.
The finale is a wild dance in fleet asymmetrical meters (lots of five with a bit of two, eight and 10 tossed in). Pegher started on a shaker, improvising against a backdrop of plucked strings, sliding low brass and bassoon chords and flurries of percussion.
She made her way back to the marimba, where she essayed a spiky theme using four mallets. Her tone was markedly pungent, rich but tightly focused. The members of the percussion section, who were nearly as busy as she was, played with verve.
A return of the first movement's music led to Pegher's lengthy, dazzling cadenza worthy of a rock drummer.
An amped-up version of the end of the first movement, now with Pegher improvising at top speed, ended the piece.
Conductor Grant Cooper handled the intricacies of the score's shifting meters and myriad cues with precision, and the orchestra matched Pegher in brilliance.
The audience responded with a lengthy ovation, with several curtain calls for Pegher and Schwantner, who attended.
Cooper opened the concert with Brahms' "Variations on a Theme of Haydn." He conducted with a light touch, letting each variation unfold simply while he held the increasingly complicated rhythms in balance. The orchestra's winds, horns and trumpets sounded glowing, while the strings played adroitly.
Respighi's "Roman Festivals" closed the program. It is brash, banal and brilliant in equal measure, when it isn't pilfering whole pages from Stravinsky (and even that is good). In short, it is a hoot that gives the players a workout.
It was the last brilliant part of a brilliant evening.
Pegher will appear with the orchestra at the Clay Center Saturday morning at 11, playing just the finale of the concerto for the Family Discovery Series. The full concert repeats Saturday night at 8 at the Clay Center.