Seeking definitive word from on high regarding my zone

Tis true, I am a neophtye stuck in the gates because I cannot even tell which zone I am in. When I saw that some zones have sub categories I havent felt such a panic since I was asked to dance the part of the snowflake in the Christmas pageant at school when I was 6. Can anyone advise. I am in Hayward, California. Its about 15 miles south west of Oakland; SanFrancisco is a bridge and 35 miles Northeast of me. My undying gratitude to anyone providing the answer that even the last resort magic 8 ball failed at providing. You can only stand so many "Looks Hazy Ask Again"

Try this site it appears you are probably in zone 10, don't worry about the a or b right now. That has a lot to do with your micro climate. I'm zone 7b, but am actually closer to an 8. It's only a yardstick.
http://images.meredith.com/bhg/pdf/gardening/hardiness/hzm_California.pdf

The Sunset Western Garden Book has detailed zone maps for California, including many sub-zones...My book shows hayward as on the edge of Zone 15 and 17. These zones are not the same as the standard usda zones as they are much more comprehensive and take into account many of california's microclimates, fog, ocean influence, etc... ...try this link.
http://www.sunset.com/sunset/Reference/GardenRef/WesternClimateZones.html

and maybe this one as well

http://www.sunset.com/sunset/web/Sponsors/Garden/sunsetmonrovia_r1/htmlfiles/zone_map3.html
though the map on the 2nd link shows you as near 8/9, the detailed map in the book shows15/17. Zone 16 is nearby but is a bit higher, has warmer summer than 17 and warmer winter than 15...all very confusing, but the maps are very detailed, and do a good job trying to balance all the various factors (I lived most my life in the digger pine/foothill belt and found the maps in the Sunset book invaluable)...good luck

I'd say you're 9b in the USDA zones, you're very slightly warmer than me in the winter but I don't think by enough to bump you into 10a, I think you really need to be on the other side of the Bay or right next to the water to hit zone 10. If you typically get a light frost or two in the winters then you're definitly in 9b instead of 10, the only time zone 10 gets frost is if we have a really unusual cold snap like we did last year.

Peaches is right that the Sunset zones are much more useful, only trouble is most people here don't know them unless they're west-coasters, and most plants don't come labelled for Sunset zones so it's helpful to know your USDA zone too. If you don't already own the Sunset Western Garden Book I'd definitely pick up a copy, it's a great reference (and it has most of the plants you might be interested in growing, so even if the nursery tag doesn't list Sunset zones you can look it up in the book and find out if it'll do well for you.)

Tryin' to find your exact 'zonation' can at times be such a pain in the @$$ .... Good eye, ecrane, you've got an excellent point which I neglected to mention, the Sunset Zones won't help much unless you have the book and can cross reference your plant with sunset's zones, but if you do get it, it is worth the money for the wealth of specificity as to what your CA microclimates are...The usda maps are more like general guidelines ....good luck !!