First thing I thought of when I read your title to your post was the Texas reports on this as well. Strange things going on all over

Maybe it was the prison at the point going up in flames
But really... I turned on the salt lake police frequencies, and didn't hear any chatter. So maybe nothing but a transformer? We Utahns know how often the power goes out around here, and with the snow fall we just got, I wouldn't be surprised if that's what it was. I watched a transformer blow near my house once, and didn't hear a boom... But it sure lit up the sky. I dunno.... All I know is I was driving home from a movie at 9:00. Was in my kitchen (which is on the ridge and overlooks the valley) making coffee 9:15-9:20, and then in my garage having a cigar at 9:25-10:15. Sadly missed what you saw...but think I would have seen it if it were huge, since the door to the garage was cracked.
Curious to know though.

Just a thought but isn't Dugway to the west of you .