Gas shut off valves are not required by law in Big Bear. Many people that buy a home in Big Bear are faced with the question of whether or not they should have one installed. Some of the insurance carriers require a earthquake gas shut off valve before they will issue home owners insurance.
As a homeowner in the Big Bear area for over 18 years, I would say that you want to do your homework on this before you have one installed.
I have sold homes to people that have had these installed and have not been happy with some of the things that can happen.
These valves are designed to shut off the natural gas in the event of an earthquake. That means they are activated by movement. If the valve closes it must be reset and you will need to relight the pilot or check to see that the appliances, heater and water heater are working after the reset. This can be hard to accomplish if you are not aware of the valve activating or the event that caused the valve to shut off. If your home is a second home and the gas shuts off in the winter, you may end up with some damage to your plumbing. 
Another type of valve (shown at the right) may be a better choice in this situation. A valve that restricts the flow, or a excess flow valve. These valve claim to restrict the flow to a safe level, but only activate if there is an increase in flow that is caused by a break in the line.
You can always just turn the gas off manually if you are at the home when the emergency occurs.
You should consult a plumbing and heating contractor to find out the pros and cons of each type of gas flow protection that is available.
Steve Hirschler
Associate, The Tim Wood Group
Coldwell Banker Mountain Gallery
42153 Big Bear Blvd.
P.O. BOX 6820
Big Bear Lake, CA 92315
steve@bigbeargallery.com
909 866-3481 EXT. 217 CELL 909 725-5889
Fax 909 866-3531