After filming the "Circle Sky" live scene in Salt Lake City, Utah on May 17, 1968, The Monkees played a brief set at Lagoon for a packed house of 5,000 fans. Micky, Davy, and Peter returned to the venue in 1986 during the 20th Anniversary Reunion Tour.
By the way, take a look at the acts that performed at Lagoon in May 1968:
May 17 – The Monkees
May 24 – The Doors
May 29 – Frank Zappa & The Mothers Of Invention / The Youngbloods / War Of Armageddon