The very end of the weekly rock column "Rock Talk From KG" in the Hayward Daily Review always included a few notes about upcoming shows, some of that not yet final or advertised. This is the final paragraph of the May 17, 1974 column, with the tantalizing note that Eric Clapton and The Grateful Dead would play together at the giant Los Angeles Coliseum, with a capacity of about 80,000. Needless to say, it didn't happen.
The idea wasn't as far fetched as it might seem. Eric Clapton had just returned to touring after a four year layoff, and his tour was a huge event. Stadium concerts were "in", at the time, a chance to see major acts in a venue with refreshments and bathrooms, as opposed to a muddy field. The Grateful Dead had a new, expensive sound system, and they needed high paying gigs. While the Dead were never as popular in Los Angeles as they could have been, even in 1974 it was well known that Deadheads would travel in large numbers, given the incentive. OK, the LA Coliseum was an old dump, and the area around it wasn't exactly hippie central, but a 4-hour Dead show followed by a couple of hours of Clapton would make it all worthwhile, right? And then we could do it all again the next day? Oh, well.
Eric Clapton did indeed play Los Angeles on July 19 and 20, but he played at the much smaller Long Beach Arena. The Grateful Dead played Selland Arena in Fresno on July 19.
As to the CSNY/Allman Brothers/Beach Boys/Marshal Tucker gig at the LA Coliseum, it didn't happen either, but it almost did. CSNY were just starting their titanic National tour, mostly in Stadiums, but the Bill Graham produced show was scrapped, and they did not open until July 9 in Seattle. The Beach Boys were on the CSNY tour, and they too opened in Seattle with them. The Allman Brothers tour seems to have been between Tulsa (July 5) and St. Paul (July 8) during these dates.
I'm listening to "Dark Star">"Have You Ever Loved A Woman">"Not Fade Away" in my mind's ear.