Fairy Ring Marasmius

Light brown. Hygrophanous (color changes with moisture). Mildly striate on margin. Notice the fine lines along the edge

Gills:

Light colored, widely spaced, not decurrent

Tough. Top often yellowish-white. Base darker from yellow to orange. Base may be slightly furry or tomentose.

White

Common in PNW grass. Often found growing in arcs or rings in lawns.

Also has white spores. Differences include:
Gills: Crowded, adnate to decurrent
Cap: not umbonate

photo: Alan Rockefeller CC-BY