What artist played as an opening act for bands like the Grateful Dead and Santana at the famed Fillmore in San Francisco in 1970?

In 1970, the artist who played as an opening act for bands like The Grateful Dead and Santana at the Fillmore in San Francisco was the iconic singer-songwriter and musician, John Prine. His folk-infused style and poignant lyrics captivated audiences, helping to establish his reputation as a significant voice in American music.