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Pyrgus comminus
Since it was seen in Northern California, I am going to go with the more widely distributed P. comminus. Comminus being a species that does exhibit variation within the species. It's a Checkered Skipper.
Well it was pretty dry in Marin County at that time of the year. All the grass was brown!
albescens flies in drier habitats and is usually paler than communis. Both occur in California. Good Luck.
Tricky one!! I think it is Pyrgus communis, although there are many similarities with Pyrgus albescens. Please, change my ID in Pyrgus sp., I will try to rule out Albenscens first.