Lake Arrowhead is covered by the San Bernardino Mountain system (system 8). This is a trunked system that covers general govt. sheriff, and fire. Lake Patrol is on there own radio channel, but I don't recall the freq. right now...
There are also conventional frequencies that you can listen to up there as well such as USFS, CalFire, and CHP. Perhaps someone can chime in with those frequencies since I don't have them handy at the moment.