Traffic, who was playing Winterland for two weekends, played on Monday morning between 9am and noon, and Jerry Garcia played with them at least for one song. The location of the temporary stage was Pier 10 in San Francisco, roughly at Washington and Embarcadero.
The Grateful Dead came over to KMPX after their Carousel show (on March 17), probably intending to play. Creedence kicked off the show, but the cops shut it down. A plan to move the event to Pier 10 was stalled, and not surprisingly it did not re-start until daylight.
The actual events are a great rock and roll story: the staff of the first FM rock station goes on strike, and the first local band to play in support of them at 3am turns out to be one of the biggest selling bands of the era. The Grateful Dead were probably ready to go on next, but the cops intervened--even so, Jerry Garcia hung around to jam with Stevie Winwood and Traffic, in itself an amazing event.(1)
Ace Parking Lot is at the site as of 2012.
Jerry performed here on
3/18/68 Traffic (KMPX Strike Rally)
1.)^Arnold, Corry, Lost Live Dead, 2010-09-03, March 18, 1968: Pier 10, San Francisco-KMPX Strike Rally, http://lostlivedead.blogspot.com/2010/09/march-18-1968-pier-10-san-francisco.html