Winning a Grammy was not the defining career moment for Indigo Girls band member, Amy Ray. Working closely with R.E.M. didn't make the mark either.

It was opening for the Grateful Dead.

Ray described the unforgettable memory that stands out most from her 30-year music career. "It was a moment of playing this huge stadium [with] 30,000 people, and we were sure nobody would be listening to us. But that's not what happened."

Adds Ray, "People really clapped and they loved us, and it felt like we kind of made our mark in some way, and were able to do something, just, really hard."

The Grammy-award-winning duo, which also includes singer/songwriter Emily Saliers, will be playing at this year's California Worldfest in Grass Valley. The four-day festival, which takes place at the Grass Valley Fairgrounds, features unique music from around the world, family activities, as well as yoga and Tai Chi lessons.

The lineup is eclectic, featuring everything from Mexican-influenced rock band Los Lobos, to Taiko band On Ensemble, or even The Skinny Singers, featuring local favorite Jackie Greene.

"Our producer Mitchell Froom thought it would be a good idea to give the fans a different perspective of the songs, and a lot of the fans wanted to hear us solo acoustic," said Ray. "Instead of having one version of the songs, he thought, 'let's do the songs solo acoustic as well, and give the fans something else.'"

Ray and Saliers first met back in elementary school, and first performed together in high school. They've been playing music together for 30 years, and have released 11 full-length albums.

Their self-titled album won the Grammy for best contemporary folk album in 1990 and 10 of their albums have reached the top 50 on the Billboard charts.

The two have also been active in a number of political and social groups, even helping to create the environmental group Honor the Earth. The group raises awareness about both Native American issues and environmental issues.

"I have passion for a lot of things [besides music], but number one would be nature," Ray said. "[Also] books, art and bicycling. I remember taking a lot of really good bike rides in Sacramento."

At the festival, the duo will be joined by a keyboard player, but will play all of their songs acoustically. Their set will be Friday night from 9 to 10:30 p.m. at the Meadow Stage.

"We just love playing at festivals, there's such a good feeling there," Ray said. "There's so much music around, so we'll be in a good mood for sure."

Advance sale prices for the festival are still in effect until July 16. Camping and non-camping tickets options are available here.