Keyed out in Aurora's Mushrooms Demystified. I admit to being surprised at this identification, because I didn't notice any black staining of the cap or stalk. But the mushroom has dehydrated somewhat, and while rains were starting to fall, the mushroom itseslf had so much duff over it that it was receiving no noticeable water yet. Cap somewhat funnel shaped, the cap edge has pulled upward so far that the gills have been pulled away from the stipe, giving this mushroom a somewhat unreal appearance. I have collected R. nigricans in this area before. Cap is quite large, about 10 inches across.