If you ever find yourself doubting the vitality and reach of the Indigo Girls, there's a video I'd like to share with you. It's a clip from a music show from the late '80s called Night Music, hosted by David Sanborn and Jools Holland and predating Holland's own long-running musical showcase, Later... Like Later..., Night Music was a show that highlighted artists and bands from all genres and periods, featuring up-and-comers mixing with veterans. The clip shows Sonic Youth covering the Stooges' "I Wanna Be Your Dog," with Amy Ray and Emily Saliers (AKA the Indigo Girls) on backing vocals.

It's a tremendously strange video, and a potent reminder of the environment in which the Indigo Girls came up. Formed in Georgia in the mid-'80s, the Indigo Girls came up in a time and a place where bands like R.E.M. were mixing jangle and folk into their rock, with liberal doses of impressionistic lyrics and individualistic spirit. It was a time of blossoming artistic intent in the burgeoning alternative scene, and the Indigo Girls came along at just the right time to become entrenched in the movement.

"When I was very young, I listened to folk," says Ray via phone, taking a moment away from her and her partner's newborn baby. "I discovered punk at the end of high school, and into community college. So, I listened to a lot of the standard singer-songwriters when I was really young, and definitely had that upbringing - people like James Taylor, Neil Young, Joni Mitchell and Carole King. But then I discovered Patti Smith and the Pretenders and all these great bands that were coming up, these sort of left-of-the-dial bands. For me, it was really moving and inspiring, but I think, as now, people listen to so many different kinds of music no matter what kind they play. There's just so much out there."

While the Indigo Girls most definitely fall into the realm of folk-rock, it isn't a stretch to hear those old punk influences in Ray's songwriting. Notably, the duo writes their songs separately, only collaborating to solidify the arrangements. If you could categorize the two, Saliers tends to err on the side of beauty and balladry, while Ray has a definite fire behind her compositions.

"That's something that's always been that way, since we started in high school," says Ray. "We just like to have our own creative space. We tried writing together a few times and it just wasn't so great. We just kind of always had our separate worlds."

Throughout their time as the Indigo Girls, Ray and Saliers have been among the most vocally outspoken political activists in the music world. Speaking out on LGBT rights, energy reform, Native American land rights, among other causes, politics naturally tend to bleed into their music.

"We (got involved in activism) when we were young," says Ray. "In Atlanta, some of the first shows we did were little benefits for homeless shelters or soup kitchens or early-on AIDS activism. As we went through life, we would meet different activists, and it was something we really cared about. My family's more on the politically conservative side of things, but they still really believed in being involved in your community. So, even though we felt differently about what that meant, I did learn at an early age that it was important to contribute."

Most heartening of all - in addition to the Indigo Girls' tireless work to use every bit of pull they have to make the world better - is the fact that these two women who met at 10 years old and started performing together at 16, are still making the same quality and quantity of music that they always did.

"We've been through a lot together," says Ray. "We both agree that we want to keep challenging ourselves and each other. ... I don't know how to describe it. It's a gift of being able to work with someone for so long. When it works, you just feel lucky."

INDIGO GIRLS, w/ Lucy Wainwright Roche, 7:30 p.m., Friday, Jan. 10, Pantages Theater, 901 Broadway, Tacoma, $26-$72, 253.591.5890