We were going to Santa Monica Beach and we decided to stop at La Brea Park.
It is a natural "brea lake" were a lot of fossils where discovered. You actually can see the metane gas coming out... we had the "luck" to see how a dove sank, so it was interesting.
The museum costs 11 dollars, we didnt visit it.
So, as I said: If you are on your way to the beach, get down the bus for 15 minutes ;)