Tricholoma fracticum  (Britzelm.) Kreisel (1984)
Syn: Tricholoma batschii

This is one of the easiest Tricholomas to tell apart -- it has a remnants of a partial veil that sticks to the stem to form an annulus. It is extremely common under Pines in the Bay Area, in parks and other urban settings. Tricholoma batschii is another name used for this species.

Partial veil remnants forming an annulus.