In an earlier post I had asked about a show scheduled for Folsom Field at CU-Boulder on August 28, 1977. Turns out it was for a festival known as "Sun Day" (this being Sun Day 3), with the following on the bill: Willie Nelson; Emmylou Harris; Dave Mason; Jerry Jeff Walker; Stillwater; Jerry Garcia. This was going to be co-organized by Feyline and the CU Program Council. I originally became aware of this through a Calendar listing in Colorado Springs Gazette-Telegraph, August 27, 1977, p. 22D.
The Boulder Daily Camera had one earlier mention that I found, regarding a hassle about the provision of emergency medical services (Linda Cornett, "Ambulance Debate Rises in Plans for CU Concert," Boulder Daily Camera, August 14, 1977, p. ??)
This didn't sink the gig, though, at least not according to published reports. It turns out that an illness in the Willie Nelson group and "personnel issues" in the JGB led to the cancellation. The notice speculates that these latter are in connection with Tutt and Elvis, the latter of whom died a bit before the scheduled gig. It also notes, however, that ticket sales had been slow. May have been win-win-win all around to cancel it. For the skinny, see "Big Concert Canceled; Borrow Some Records," Boulder Daily Camera, August 19, 1977, p. 17.
I plan on poking through the Program Council archives to see if there's more to the story, just for giggles.
update--here is the article