Turns out both grow in my area, and look identical to this when young. Yikes! So based on a post yesterday, I took this outside and sliced it in half. So far it looks promising (I think?) and I’m not dead yet.
This was found growing in a Colorado yard near the base of an elm tree, in an area where there are also rotting cottonwood roots. Altitude is right at 5000 feet. It wasn’t my yard so I’m not sure how many days it may have been growing before I picked it today. I have put both halves in the fridge for now, is there any other information I can provide to help identify it?
A full size copy of the inside can be viewed here: http://sourpuss.net/projects/mycology/2023-08-13/IMG_7239.JPG
It’s too bug-eaten to tell if it’s all-white on the inside. I would avoid it because you can’t really sight-ID it.
Also the shell around the outside is too thick (should be eggshell thin) imo there’s a good chance it’s an Earthball (also poisonous, but not destroying angel poisonous).
Get Mike Beuge’s dichotomous key, it’ll really help you not die.