The grandfathers of screaming double lead guitars -
Illinois Speed Press (1969)
https://www.youtube.com/watch?v=9TCs9B7nA34I think I saw them at the 3 day Sound Storm Music Festival (it was 1970 after all) in Poynette, Wisconsin.
https://www.wisconsinhistory.org/Records/Article/CS374"About 30,000 people attended Sound Storm, the majority sneaking in through the woods without paying (that's what we did). The Columbia County sheriff, seeing his officers exponentially outnumbered by hippies and bikers, wisely decided to ignore misdemeanors such as nudity and drug use. LSD and other psychedelic drugs were everywhere, along with marijuana and cheap, screw-top wine. Medical students staffed first aid and "bad trips" tents, volunteers from the Hog Farm commune in New Mexico helped as stage announcers, and Madison's Mifflin Street Co-op provided free food."

Poynette, Wisconsin. Side view of the Grateful Dead on stage, featuring Bob Weir, Mickey Hart, Phil Lesh, Jerry Garcia, and Bill Kreutzmann, play on stage at the Sound Storm Festival.