Stropharia rugosoannulata

Common Name: None.
Description: Cap 5-20 cm across, convex-flattened to umbonate; deep purplish red to dull brown or even grayish or even white with age; smooth, not viscid. Stem 100-180 by 10-25 mm high and wide.
Habitat: On wood chips and bark mulch and around flower beds. Very common. Found widely distributed in Northern America.
Edible: Delicious.

Source: Mushrooms of North America by Roger Phillips.