That tour appears to have followed a fairly regular path, counterclockwise out of Boulder. Similar to:
https://flightaware.com/live/flight/...210Z/KBJC/KBJC
Though flightaware doesn't show it, flightradar24 shows a sudden turn to the SSW in the last minute, and a 1000 ft drop in close to half a minute.
https://www.flightradar24.com/data/a...337kn#2caf3cca
Ground temp was 83F, about normal, in recent years. Low humidity. Low wind.
Perhaps an engine was lost, and being between ridges, at about 9k ft, with one engine and 3 passengers and full fuel would be very undesirable, even with a turbo. Though I suppose they were nowhere near critical altitude, so single engine performance shouldn't have been much affected.