I was thinking it was a deer also and maybe our dog spooked him off before he finished his meal. We have a lot of blacktail deer here. They eat everything, and our landscaping reflects their appetite.
Thanks for your input and narrowing it down to agaricus. Agaricus augustus seems more prevalent in our area and matches the description on local online sites. This species is apparently edible but I’m afraid this particular one is well past its prime picking time.
Absolute unit on the west coast (lemmy.ca)
Banana for scale. I was a little late to the party as it looks like something munched on it....