Recent changes in state law require that homeowners in certain high fire risk areas maintain defensible space clearance out to 100 feet from their home, expanded from the 30-foot firebreak that was already required.Even if you are not in a high fire risk area, it’s a good idea to create enough defensible space around your property to decrease the risk of fire.
Here is a link to the brochure of the CDF's guidelines for creating defensible space: http://fire.ca.gov/cdfbofdb/PDFS/4291finalguidelines2_23_06.pdf
For more information, the CDF website is http://www.fire.ca.gov/