They are adding to that total this fall, bringing along Bonnie Raitt, Indigenous and special guest Joan Baez for a series of four Honor the Earth benefits in Montana.

The tour launches September 30 at The Shrine in Billings before moving on to Great Falls, Bozeman and ending in Missoula on October 4.

Honor the Earth – which counts buffalo protection and restoration among its prime projects – reports that state and federal officials have killed more than 2,500 buffalo outside Yellowstone National Park over the last four years.

The Indigo Girls have raised more than $465,000 over the years for the group, which has distributed grants to 65 Native American groups for environmental defense, sacred land protections and restoration of sustainable communities.

“As non-Indians, we cannot sit by silently and watch the continued destruction of Native communities,” the Indigo Girls said in an open letter. “The basic issues of human rights, justice and our own survival are ultimately at stake.”

In addition to the Honor the Earth benefits, the Indigo Girls will stay on the road through October, stopping at a number of colleges. The tour coincides with the October 3 release of a 16-track Indigo Girls collection titled A Retrospective.