I live about 12 miles west of Concord. Not any pure electronics hobby type stores there that I know of. There is of course Best Buy and a hugh Fry's in town. If your into R/C hobby stuff there is a very nice and large Hobby Town next door in Walnut Creek: Google Maps
Silicon Valley is probably a good hour+ drive away if there is no traffic but there are sure to be something there in electronics surplus, I just don't like the traffic anymore and mostly mail order.
Lefty