California Earthquake Faults is an iPhone/iPad app that shows your current location or a location you specify, the closest major California faults and approximate distances to those faults.  There are 5 main screens (see below):

Fault Maps Current or found location, faults in the selected area and names/distances to the closest 4 faults.
Distances Names, distances and color coding of the closest 44 (iPhone) or 70 (iPad) faults.
Find Find the nearest faults to a location you specify.
Info Basic app info.
Settings View and adjust app settings.

California Earthquake Faults shows the vast majority of faults in California the USGS classifies as "Historic" (active in the last 150 years) and "Holocene to Latest Pleistocene" (active in the last 15,000 years). That includes over 115 faults and 248 fault lines (some faults have multiple fault lines). It does not include all faults or faults classified as "Quaternary" (15,000 to 1,600,000 years) by the USGS. All fault lines and distances are approximations.

The current version (3.03) is available on the App Store (here) for $1.99. It requires IOS 12.0 or later and an active WiFi or cellular services (preferably both) that allow secure connections to the Internet. Some public WiFi networks do not allow secure connections. In this case, you can turn off WiFi and use a cellular network (if you have cellular services).

The current version (3.03) works with iPhone SE, 5s, 6-8, X, 11 and iPad mini 2-4, Air 1-2, 5th Gen, 9.7" Pro, 10.5" Pro and 12.9" Pro.

(1) We have another app called U.S. Earthquake Faults that covers the continental United States. It's described here and available on the App Store here.
(2) Under certain conditions, Location Services doesn't work properly. You can work around this problem by: (a) turning Location Services off and back on (Settings, Privacy, Location Services), and/or (b) setting Location Services, Cal Faults to "Ask Next Time" (Settings, Privacy, Location Services, Cal Faults).


Shows faults near the current/found location, faults in the San Francisco Bay Area, faults in southern California and faults in California. Shows distances to the 4 closest faults and allows zooming into them (like San Andreas below). Tapping a fault with show its name.

Current Location
San Francisco Bay Area
Southern California
Zoom into San Andreas fault
Bay Area
Bay Area
So Cal


Distances shows distances to closest 44 (iPhone) or 70 (iPad) faults.
Find allows searches for specific locations.
Info shows basic app information.
Settings shows and adjusts app settings.


A few settings require explanation:

- "Describe Selected Fault" controls whether or not a fault name is displayed when you select one of the 4 closest faults.
- "Describe Found Location" controls whether or not a location name is displayed when you use the Find function.
- "Method" controls when the map display is updated when you are moving.
     - "Auto" automatically updates the map display so the current or found location is visible
     - "Always" updates the map display everytime a location update is received (more accurate than "auto" but uses more power)
     - "Manual" doesn't update the display


If you live near faults included in this app, you can locate faults (approximately) by driving over them.

The first screenshot was taken while approaching the Napa fault on Highway 121/12 in California. The second screenshot was taken while driving right up to it.

San Francisco
San Francisco


Comments and questions are welcome. Contact me at You will get a response.

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