Also, REACH 1 has a Satellite Phone in between the seats (or the pilot's seat and the gurney I remember the cockpit of the A109 looking pretty cramped). They have a company dispatcher at STS but they communicate all their initial dispatches or flight following of the fleet primarily via the satellite phone from what I've heard. I noticed someone submitted a company freq for them on 131.875 Mhz - does anyone know if this is primarily used between the pilots or if they have a base station for it at STS so dispatch can talk as well? Next time I'm up there I'll have to give it a listen.
Once airborne and responding to a scene, they'll check in with the county comm center they're headed to. SAR2401 says in Sonoma County thats REDCOM dispatch (and then they'll be directed to a relevant Control or Tac). In Marin County we often use REACH 1 as well (or CALSTAR 1 from CCR), and even though Marin is primarily digital trunked they check in on "MARIN 17" 155.10 PL 114.8, which is used as a mutual aid channel between comm center and outside EMS agencies. They might start using "Marin Local" on 151.04 PL 146.2 as that's a new CAL FIRE mutual aid frequency with the Woodacre ECC of Marin Co Fire (which used to be loband).
Regardless of the frequency, REACH 1 will check in with the county comm center first, obtain updated information about the conditions and location of the LZ, provide an updated ETA, and obtain ground contact information and a frequency. Ex: "REACH 1, LZ is (lat/long coordinates), your ground contact will be Engine 621 on CALCORD, do you have an updated ETA?" or often "REACH 1 you've been cancelled thanks anyway for your help!"
When the pilots switch to CALCORD they talk simplex directly with the units who have prepared the LZ and get some general geographic and weather information and any pertinent hazards. The pilots usually make a pass over and inspect the LZ (with the spotlight especially at night), fly a small traffic pattern and land, advising the units on the ground what they're doing and when it's safe to approach.
Hope that was helpful,
-Inigo