Think about the body clock as a human version of the one on your smartphone. If you turn off the phone when you board a plane in New York and turn it back on when your flight lands in Los Angeles, you will notice that the clock automatically adjusts the time to reflect that you're now in a different zone. In the same way, your body clock will eventually adjust to the new light/dark cycle on the West Coast [source: Newitz].
Anyone who's ever suffered from jet lag knows that the shift doesn't happen right away. Your body has been trained to release melatonin at a certain time each night, and will initially continue to do so even when the optic nerve tells the brain that it's still light outside. Eventually however, and your brain will time the melatonin release to the darkness. In other words, the clock slowly rewinds itself to reflect the rising and falling of the sun and to ensure that you don't spend all of the prime California beach time snoring in your hotel room [source: Newitz].