I think that would be a very tall order. I've seen maps of portions of the Angeles National Forest pre-attack plan. It shows water sources, helispots, maintained fuel breaks, access characteristics and some others that I've forgotten. There are a lot of helispots on the Angeles and I believe L.A. Country uses most of them for the air evacs that are so numerous on the Angeles. The traffic accident, search and rescue and medical workload is very heavy. I have no access to the Angeles information so getting the county's info would probably be very hard. Due to terrorism concerns, real or perceived, a lot of aviation related information is guarded.
However, some people find some incredible information using Google. They take a long time to find little gems here and there. Maybe someone will step up to the plate here.
Andy - you might want to check the FILES section at SoCalFire or SoCalScan at yahoogroups - or maybe at the LA County fire buffs website. I vaguely recall having seen a LA County LZ map in the past (maybe 5 or 6 years ago.)
Get the application on the link above called "helispots" it's the counties official fire fighter app with helipad locations including coordinates, special instructions, Landing surface type, etc. it's great an should be what youre looking for.