Collection location: Los Trancos Preserve, Palo Alto, Santa Clara Co., California, USA [Click for map]
Calling this one A. sinapina mostly because of the yellowy veil tissues found on the esges of the cap. More were found last year like that, then this year.
But I saved these, and I might try to work up some micro details on them. There seem to be a few difference between this and A. gallica, which these might also be.