The Grisette is a species in the genus Amanita, a group that contains a number of deadly mushrooms. Unlike most of the other Amanitas, this mushroom lacks a ring on the stem, even though it emerges from a sac-like volva in the ground.
Young specimens emerge with an oval cap, which eventually becomes umbrella-shaped or flat with a little bump (called an umbo). In this species, the cap is gray to brown and the margins of the cap are feintly lined (striated), suggesting the presence of gills below. If you turn the cap over, you will see that the gills are white in color and free from the stem. In a closely related and local species called the Tawny Grisette (A. fulva), the cap color is orange brown. Some of the darker colored mushrooms in the photos below are probably Amanita fulva.
The grisette does not grow on wood; it is mycorrhizal with hardwoods and conifers. Look for it spring through fall in the woods or even on lawns in urban areas.