I would like to exchange a few dollars for yen here in US before traveling to Japan.
San Francisco Bay Area------Where?
I think it's wiser to change at the arrival airport, not in USA.
If you want to get a small amount before arriving to Japan, just go to your bank and get yen. Some banks may not have yen cash at hand but will order it for you. Don't worry about the poor exchange rate in the US, you'll only lose 2-3 dollars at most if you're exchanging a small amount.
IF you have an account with Wells Fargo ask which of the branches has foreign currency and get it there. They usually have yen on hand or you can order it.
I always like to have currency before I arrive and the difference for me between getting it from Wells Fargo and getting it at an ATM in Japan is a small number.
If it helps at all, If you're arriving at Narita, there are about 5 ATMs that you will walk past before there's anything yo walk past that you can spend money on, so technically there's no need to have money in your pocket before you arrive.
I usually get a minimal ($25) amount of Yen before I leave. I use the Wells Fargo Marina or Financial District branches. Then I use my ATM card at 7-11 cash machines while I'm in Japan. Exchange rates at banks and currency exchanges are not good.
Travelex has about the worst rates you can find. Avoid them.