Panaeolus foenisecii
This common lawn mushroom pops up after rains. Cap can be two-toned and
varies in color from brown, gray and tan; sometimes with purplish shades. Gills
are often mottled (little splotches of white on dark gill face).
Appearing in large numbers at times. If you want to eradicate this mushroom
from your yard, here is Michael Kou's advice, "...the short answer is: you can't
get rid of them. If you are worried about mushrooms ruining the appearance of
your lawn, I suggest you rethink your priorities in life."