Install Crestmap as a Home Screen web app first. On current iOS versions, the option can be buried in Safari's menus:
Crestmap can notify this iPhone when it discovers a new incident matching the areas and categories you choose.
You stay in control: choose all Forest roads, Crest + west forest only, or Malibu roads; select incident types; and turn alerts off here at any time.
Choose which newly discovered incidents should notify this device.