CHEYENNE, Wyo. (AP)  The American Civil Liberties Union said on Saturday that it would investigate the actions of federal officers who had arrested five members of the Rainbow Family in western Wyoming during the group’s annual gathering.

The federal Forest Service said a mob of about 400 members of the Rainbow Family, a group of hippie types and eccentrics who hold a weeklong national gathering on public land each year, threw rocks and sticks at Forest Service officers who tried to arrest a member of the group. The agency would not give a reason for the original arrest.

About 60 federal and local officers responded, Forest Service officials said, and fired pepper balls  pellets that disperse a pepper solution  at the crowd.

As many as 7,000 members of the Rainbow Family camped out this year on Forest Service land.

Linda Burt, executive director of the A.C.L.U.’s Wyoming affiliate, said on Saturday that the organization planned to accept collect calls from Rainbow Family members for the next two weeks to hear their version of events.