The River Prairie Minstrels, who perform at Mojo's at the River Music Experience the first Saturday of every month, will play from 6:30 to 9 p.m. Saturday.

The group has about 42 members, and they show up without notice at the performances.

Bill Schaumberg of Coal Valley is the stage manager, and he said. "It's very informal. Whoever shows up plays on a given night."

Some of the musicians who usually participate are Will Trotter, Rock Island, who plays guitar and sings traditional folk music, and Cathy and Jerry Wetzel, Bettendorf, who play guitar and perform Ms. Wetzel’s original material. Mr. Wetzel does the sound for the group.

Guitarist Ed Longenecker, Davenport, sings mostly the blues, and Mr. Schaumberg sits in with him and plays harmonica.

Steve Chesley, Bettendorf, plays guitar and sings contemporary rock, and he also performs with Lyle Stratton, Bettendorf, who plays acoustic guitar and sings contemporary rock.

Mark Ridolfi, Rock Island, plays rock on acoustic guitar.

"A lot of them have acts," Mr. Schaumberg said. "Will Trotter performs with his wife, Pam, who plays penny whistle."

Admission is free on these Saturdays.

Mr. Schaumberg said, "We want to encourage people to perform. If somebody shows up with a guitar, we put them onstage. We encourage people to come and join us. We have a good time."

The group was founded in June 1993, starting with coffee house performances at the Rock Island Library, and moved to Mojo’s in 2005.