These are called frost flowers. A google of this term will bring up a bunch of cool photos. I think they can occur anywhere it freezes, but I've certainly never seen any that big. I'm used to seeing them from the stems of recently cut or recently frosted weeds and stout perennials, early in the winter while there is still some sap in them. And one has to get up early to see them....once the sun is on them they quickly melt or evaporate away.....
I'm almost never at the property during freezing weather. So, for all I know, I may have frost flowers every winter. I'm going to try setting up the perfect conditions for this, when I'm back on a cold day.
Found one more picture on my phone. Next time we do a calendar, these things will be submitted. My good camera should surpass these cell phone shots.
These are probably the last frost flowers for this year. We did not get frost last night.
I've determined that they develop on the same pieces of wood every night. Half rotted and saturated pieces of alder are the main producer. The largest one where my hand is showing, bridges a small depression. Wet wood in full contact with the ground, doesn't always get cold enough.
It's coming up to that time of year, when these things are likely to be observed.
I still haven't seen these anywhere else except for a little thing the size of a dime. So I think it was a fairly rare occurrence. The combination of warm days and cold nights, with rotten pieces of alder and cottonwood, containing enough moisture to allow continuous growth of the frost. Cold enough to make frost but not so cold that the whole piece of wood freezes, which I believe would shut down the process.