This large, showy fruiting body is one of the most common causes of mushroom poisoning in Arizona, both of people and pets. It grows enthusiastically in irrigated lawns, even in the lower desert areas like Phoenix and Tucson. It is also found quite frequently in other states, and mycologist Dr. Michael Beug has declared it the most common cause of mushroom poisoning in the entire U.S.A.
Inexperienced collectors frequently mistake this conspicuous mushroom for desirable edible species like the Parasol (Macrolepiota procera), Shaggy Parasol (Lepiota rhacodes/Chlorophyllum rhacodes), Meadow Mushroom (Agaricus campestris), or Shaggy Mane (Coprinus comatus.) It is not deadly poisonous, but might make you wish you were dead if you make the same mistake. Typically it produces hours or days of highly unpleasant gastrointestinal distress, and is severe enough in some cases to require hospital treatment.
The greenish gills and spore print are the key to identification, along with its saprotrophic ecological niche that does not require a mycorrhizal association with any tree roots. Also, the scales on its cap tend to be confined to the central apex, rather than extending out to the edge of the cap as is typical for Lepiota and Macrolepiota.