Hi Kristine,
The High Sierra Striders is a solid running club based in Mammoth Lakes. They do not seem to have any direct involvement in the race that you a training for, but they are involved in several local races each year in Mammoth. They sould be very familiar with the concerns of runners coming up from lower elevations to race. Their president and coach, Andrew Kastor, is quite approachable and might provide you with some insights. His contact info is on the club's website
www.highsierrastriders.org.Andrew's wife is Deena Kastor, Olympic bronze medalist in the marathon. She trains and assists with the club activities in Mammoth. She could also have some insights for you.
I live at sea level and ran the Wild Wild West 10 mile trail race in the shadow of Mt Whitney this May 5. This race ranges from 4600' to 6300' elevation. I camped at Whitney Portal the two nights before the race and that seemed to work for me. I like to run up the Meysan drainage directly from the family campground.
By the way, another (and established) half marathon is coming up in Mammoth August 18, the Quake and Shake Half Marathon. I believe its entry fee is about a quarter of the amount charged by the San Diego people.
Good luck in your race preparation.
Jim F
PS: The Whitney Portal Store pancake is a great carbo load! Thanks Doug.