Professional-quality record tapes from Neil Young and Joni Mitchell's 1968 Michigan Concert have been recovered.
The recordings were found at Canterbury House by Michigan History Project.
A live performance by the pair was recorded on the University of Michigan campus, a venue that regularly hosted popular counterculture artists in the 1960s.
"They were in the possession of a private collector. Then they disappeared, and we were afraid they were gone for good. But a few weeks ago they resurfaced, much to our surprise and relief," MHP president Alan Glenn said in a statement to Rolling Stone. The non-profit organization said its first priority will be to get the "historically significant" material transferred to a digital format, and "make sure that the original analog tapes are safely archived."