This website says that you can run the full marathon for the start of the Triple Crown. And this if copied from the Carlsbad Marathon's FAQ's page:
What is the Half Marathon Triple Crown and how do I qualify for it?
A trio of Southern California half marathon race directors have formed an alliance to create a Half Marathon Triple Crown award to honor participants who finish all three half marathons in the same calendar year.
In addition to the Carlsbad Marathon/Half Marathon, the threesome includes the La Jolla Half Marathon and the America's Finest City Half Marathon.
To qualify for the Triple Crown, simply register for and complete (within each event's time limit) the Carlsbad Marathon OR Half Marathon, the La Jolla Half Marathon, and the American's Finest City Half Marathon all in the same calendar year and we'll take care of the rest! Special commemorative medals will be waiting for all who qualify at the Triple Crown booth located at the finish area of the America's Finest City Half Marathon.
8/31/08 Nike+ Human Race 10K - 56:47
10/18/08 Nike+ Women's Half Marathon - 2:06:12
1/25/09 Calrsbad Half Marathon - 2:02:36
4/26/09 La Jolla Half Marathon - Registered
5/31/2009 San Diego Rock 'n' Roll Marathon - Registered
6/13/2009 Camp Pendleton 10K Mud Run - Registered
8/16/2009 America's Finest City Half Marathon - Registered
| Pounds lost: 7.0