The NIFOG designates VSAR16 along with some of the VFIRE channels and the two VMED freqs as: VHF PUBLIC SAFETY MUTUAL AID AND COMMON CHANNELS
These frequencies are licensed for various uses in many areas of the US. Actual usage varies greatly.
Former CA SAR volunteer here. 155.16 MHz has historically gone by "MRA", "NATSAR" (short for National Search & Rescue common) and many other names prior to the formal VSAR16 designation in NIFOG.155.1600 is used all over the western U.S. for search and rescue. When I lived in California in the Sierra Nevada foothills late Hubby and I could hear it quite frequently. In some western counties, it is the only SAR frequency they use. It is commonly known as "MRA" - Mountain Rescue Association. It was something Hubby and I included in nearly all of our scanner files, except those for big cities, which we tried to not use.