For peak summer travel, fly from Oakland to Washington DC for $282 roundtrip on Southwest. If you're in the capital and want a little California sun this summer, this fare is also available from Washington DC to Oakland.
Searching Southwest.com, I found seats departing Oakland OAK on Tuesday, July 17, returning from Washington DCA on Tuesday, July 24.
Other dates are also available for travel on Tuesdays, Wednesdays, and Saturdays, from July through early November.
Good news if you travel with checked bags. Southwest includes two free checked bags on all fares. There are also no change fees if you decide to change your flight. Fare difference may apply.
Need a room in Washington? Here's what's available for the above dates on Hotelwatchdog.