I had the good fortune to see Santana at Tanglewood in western MA on 8/18/70. At the time, the Abraxas album, their second, had been out for a few months and was getting a ton of FM air play. The show featured many of their classic tunes from this album--Black Magic Woman/Gypsy Queen, Oye Como Va, Incident at Neshabur, Se a Cabo, Hope You're Feeling Better, as well as songs from their seminal first album. This is the original line-up, the same one that played at Woodstock. The whole concert was video taped and uploaded to YouTube about a year ago. The video isn't very good (though far better than much of the cell phone crap you see there) but the audio is amazingly good:
BTW, they opened for the headliner, Miles Davis.