|Or possibly Agaricus moelleri|
Moelleri, however, does not have pink gills, which these specimens seem to have.
Hondensis is said to have "pinkish" gills when young, and the stipe is said to exhibit a phenolic odor (as does moelleri) which these specimens exibit. The stipe base of hondensis is also said to bruise light chrome yellow which this one seems to do. Hondensis is also said to prefer forested habitat, which is where I found these specimens.
So, despite it's pink gills (suggesting a Meadow Mushroom) and despite it's marshmallow shaped cap suggestive of moelleri, I will, for now, go with Agaricus hondensis.
Moellari is said to stain bright yellow at the very base of the stipe (the base of the three specimens I found were punky and beginning to rot so I could not use this test) and moellari sounds like it is more common, but still, I will stay with hondensis based on the colour of the gills.
I am open to comments from anyone who knows these mushrooms better than I.