Long tailed field mouse (apodemus sylvaticus) in California?

Question

I'm trying to identify the mice in my backyard in a semi-rural area of Ventura County, southern California.
They are smaller than a house mouse, and they live in burrows in the lawn. They are plain brown in color, with long black tails.
Sometimes I'll see one climbing a grass seed head.
They are pretty numerous most of the year. If I place a bowl or bucket upside down on the grass certain times of the year, I will see one or more mice under it when I pick it up. I've never seen one in the house, though they could easily get in. I am not aware of them doing any damage.
The only mouse I have found that really looks just like them is the long-tailed field mouse of Europe. Have they also settled here, or is this a native species? It seems to me the black tail is kind of distinctive.

They're not deer mice; I know deer mice. I used to have one as a pet; a very pretty mouse, with lovely eyes, bigger than a house mouse. But now they can carry hantavirus, even in Ventura.
My mice are darker and plainer than pictures I've seen of harvest mice, but maybe a local variation...

I think you are right, they are harvest mice.

Answer 1

Maybe a Western Harvest Mouse or a Deer mouse. Both are pretty common in So. Cal.

Harvest mouse:
http://www.visualsunlimited.com/images/watermarked/305/305759.jpg
http://www.escape.org/lwm/albums/album100/WHMouse_6_7g.sized.jpg

Deer mouse:
http://www.funkman.org/animal/mammal/deermouse.jpg

Answer 2

California Field Mouse

Answer 3

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