Sure. First, let's be clear about one thing. Activating your Spot or Inreach, is not the same thing as activating SAR. To keep it simple, Inreach and Spot will activate a response to your emergency in the form of law enforcement and medical services, via GEOS (then forward to 911). Since Spot and Inreach know exactly where you are at, it has nothing to do with Search and Rescue (SAR). With that said, I suppose a Spot activation could turn into a SAR mission at some point if the first responders were unable to locate the person who activated their device.
Now, as far as San Diego is concerned, and most other areas I'm aware of, a SAR mission will be initiated after several key members have assessed the situation and determined a SAR call-out is warranted. It will almost always start with a call to law enforcement. Usually in response to a missing person obviously (but there are other missions we handle). The reporting party will provide details to the responding officers/deputies. The deputies will advise a supervisor. The supervisor will determine if a call to the SAR coordinator is warranted. The SAR coordinator will then assess the information and make a final determination if there will be a SAR call-out, and if so, which resources. We have several different assignment groups. Not all will be sent all the time.
Once SAR has been activated, team members will start showing up within about an hour anywhere in SD. The team members on the scene will start collecting pertinent information and establishing a place to set up a command post. Resources like the actual command post might take up to two hours to arrive. A supervisor will put together a search plan and start sending out teams.
So, to summarize, let's say you are out in the desert and riding with a group of friends. One person goes missing. You get to the point where you need to call for help. Start by calling 911. The deputies or officers that arrive on the scene will assess the situation and make a decision on whether or not to start the SAR process.
Anyone have any questions about San Diego Sheriff's Department SAR, let me know.
BTW, we do have a dual sport response team, which I am a member of. I also am field certified for searches and a member of the motorized unit, which provides transportation to search teams in remote areas via 4x4 vehicles.