Historical Seattle Shows:
7/1/79 - Seattle Center Coliseum, Seattle (another awesome show!!)
5/21/74 - Edmundson Pavillion - UW (awesome show!!)
All Recorded Shows:
- Internet Archive List
8/20/69 - El Roach, Ballard
8/21/69 - Greenlake AquaTheater guest appearance on flute, Charles Lloyd.
youtube link to show recording: Click Here
1/5/70 - [venue], Seattle, WA: Grateful Dead [unconfirmed]
Another blogger pointed out that Tom Constanten mentions the Dead playing the Aqua Theater in Seattle on January 15, 1970. While this is clearly a spurious venue--the Dead had played the final show at the Aqua Theater on August 21, 1969--I wouldn't discount the date. Constanten has clearly been using a diary or some other form of reference, and some of his most interesting dates fit very clearly into the Dead's touring schedule, even though they are unremarked elsewhere (for example, September 16, 1967 in Las Vegas).
Although January 15, 1970 was a Thursday, I would not at all rule out that there was at least a show scheduled in Seattle, even if it wasn't played.