Collection location: Howarth Park, Santa Rosa, Sonoma Co., California, USA [Click for map]
I think this must be a clitocybe. There were several. Forgot to write the trees but I believe there were Douglas fir, oak for sure and possible manzanita. I’ll have to check. Pileus was 2.7 cm across, stipe .4 cm at apex, total height 5 cm. Note the very coarse and curly mycelia at the base of the stipe.
Using the key Darvin suggested, I agree that this is most likely C. foveolata (I’m guessing the missing v in your comment was a typo), right down to the “stipe base with abundant or conspicuous rhizomorphs”.