Walnut Creek is in Contra Costa County. Therefore it is entitled to use the Contra Costa County designation.
Contra Costa lies within the larger San Francisco Bay AVA, which in turn lies within the massive Central Coast AVA, so either of these are valid.
A winery using fruit from Walnut Creek may use any one of these designations, however the TTF generally doesn't allow wineries to name multiple AVAs, so if the winery put Central Cost they probably won't be allowed to state Contra Costa County (and vice versa). However they would be allowed to use the vineyard name.
Concord,CA and Walnut Creek,CA
The Infrared Data Association was incorporated in Walnut Creek, CA. The corporate address is P.O. Box 3883, Walnut Creek, CA. Their website is www.irda.org.
Here is the detailed listing of 34 trailer rental companies from Walnut Creek: http://local.sanfrancisco.com/walnut-creek+ca/car+rental/distance.30.26060501.all.zq.html
cost plus
The address of the Lindsay Wildlife Museum is: 1931 1St Ave, Walnut Creek, CA 94597-2540
The address of the Ruth Bancroft Garden is: 1552 Bancroft Rd, Walnut Creek, CA 94598-2361
The address of the Philippine Folklife Museum Foundation is: 305 Drayton Ct, Walnut Creek, CA 94598
The address of the Shadelands Ranch Historical is: 2660 Ygnacio Valy Rd, Walnut Creek, CA 94598-3445
It is 418 miles according to Google Maps.
The Ygnacio Valley Library is located at 2661 Oak Grove Rd, Walnut Creek, CA 94598.
The address of the Walnut Creek Library is: 1644 N. Broadway, Walnut Creek, 94596 4297
The address of the Massilia Foundation For Art And Culture is: Po Box 2608, Walnut Creek, CA 94595-0608