Knowing your zip code's 4-digit extension allows OpenCongress to find your Representative and allows you to find other users in your Congressional district. Don't worry if you don't know it offhand -- you can look it up easily on the U.S. Postal Service site.
about 4 years ago.
OpenCongress California Group State Group 22,559
Congressional District Group
OpenCongress CA-25 Group District Group 254