Get incident alerts on iPhone

Install Crestmap as a Home Screen web app first. On current iOS versions, the option can be buried in Safari's menus:

Open Crestmap in Safari, not an in-app browser.
With Compact tabs, tap More (…), then Share. With Bottom or Top tabs, tap Safari's Share button directly.
Scroll down the Share sheet and tap Add to Home Screen.
If it is missing, scroll to the very bottom, tap Edit Actions, then add Add to Home Screen.
Turn on Open as Web App, then tap Add.
Open Crestmap from its new Home Screen icon. Open Alerts from the menu and choose what you want.

Turn on incident alerts?

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.