A little recognized portion of FCC Part 97 regulations applies to 420-450 MHz operations in most counties in our Sacramento Valley section:
47 CFR §97.313 (f) No station may transmit with a transmitter power exceeding 50 W PEP on the UHF 70 cm band from an area specified in footnote US7 to §2.106 of part 2. The indicated affected areas are specified in http://transition.fcc.gov/oet/info/maps/us7/, in the State of California within a 240-kilometer (150 mile) radius around locations at Beale Air Force Base, California (latitude 39°08′ North, longitude 121°26′ West).
More information on the additional impact on 70 cm repeater stations is at http://www.narcc.org/NARCC-ARRL-PAVE-PAWS-Update-2014a.pdf
The Amateur Radio Service shares the 70 cm band on a secondary basis with the US Government which has priority. The US Department of Defense routinely monitors and locates signal sources on these frequencies. Our voluntary cooperation is mandatory to avoid interference with the Pave PAWS (Phased Array Warning System) radar at Beale AFB and thus to assure our continued access to these frequencies.