I witnessed some of them form

August '89. i was a pizza man. Rarely got out before 2:30 am. i used to go to this park to wind down and watch the planes. This park is right by the airport. Maybe judgemental, but i would give each one a score on takoffs and their landings.
But here's the deal. I just happened to be looking in the right direction at the right time. A streak of light came down and turned into a shower of sparkles. I went to investigate armed with two flashlights and a bb gun. It was that thick sticky sagebrush type of stuff. Then I saw them. Multiple bowl shaped swirls that looked singed and the area smelled like ozone.
Some were overlapping. The biggest one was about 40 feet across. it had a smaller one intersecting it.
Never found any evidence. I was hoping to find a big rock. Found nothing but twirled sagebrush. Now that area is a high end housing development.
I can say that even as fleeting as it was, it was cool.