Exercise #4 (1973), opening bar. This example stems from Road tapes, venue #2, not yet released at the time Brett wrote his response.
Call any vegetable (1971), opening of the solo. The A7 chord upon an A pedal is strongly present. This solo begins in A Mixolydian with a C# dominating, soon to move over to A Dorian with a C natural.
The Gumbo variations, opening. In his response Brett writes about the Gumbo variations: "this is simply the blues scale in G, not clearly Dorian or Mixolydian". I agree that this song is mingling Dorian and Mixolydian. The intro from above obviously has the accent upon Mixolydian, the only scale that supports a Mm7 upon its tonic. Also Andy Aledort is indicating G7 in the Hot rats guitar book.
Promiscuous, opening. Here an open tritone is used (staves 2 and 3: F#-C), making the overall D7 chord sound more dissonant than usual.
Red tubular lighter, section with in bar 4 an A7 chord in an A Mixolydian environment. This example stems from The Mothers 1970, not yet released at the time Brett wrote his response.