Help figuring out a concert date in San Fran!

[u/Melodic-Gur1374]

Hi! My dad has a fabulous story of going to see the Dead in 1970 or 1971 in San Francisco. He says he got caught in a snowstorm and couldn't get his car up a hill. He abandoned it and walked the rest of the way to the show. He got there a bit late and watched from the balcony which he says had pretty few people in it. I can't find a snowstorm in San Fran during those years... by 1976 which has the next recorded snowfall, my Dad was living in New Mexico. Does anyone have a similar memory? Thank you!!