This would be better asked in the California Forum as they are most likely communicating on the Placer Co LE channels, except for app/dep comms with the ATC. Just click on the report link and ask for it to be moved.
There are several helicopters and several places you might pick up radio traffic. The incident you want could be CHP or Placer Sheriff (or on one of the local police channels). One frequency we all listen to that gives us "air co-ordination" is called Metro Air 132.125 AM. While that has interesting comms, it's unlikely you'll hear an actual incident there. It's pretty tough to just log in cold turkey and know where something is happening. You'd need to have several channels/frequencies programmed and scan them when something is happening.